Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.29   12.317%   $224.9597   $224.96   $224.95   $225.00  
  Purchase #2 $111.65   3.298%   $115.3322   $115.33   $115.35   $115.30  
  Purchase #3 $183.93   3.237%   $189.8838   $189.88   $189.90   $189.90  
  Purchase #4 $101.29   12.231%   $113.6788   $113.68   $113.70   $113.70  
  Purchase #5 $243.84   6.659%   $260.0773   $260.08   $260.10   $260.10  
  Purchase #6 $153.53   8.788%   $167.0222   $167.02   $167.00   $167.00  
  Purchase #7 $122.50   4.866%   $128.4609   $128.46   $128.45   $128.50  
  7 purchase totals = $1,117.03       $1,199.4149   $1,199.41   $1,199.45   $1,199.50