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 $200.50   5.689%   $211.9064   $211.91   $211.90   $211.90  
  Purchase #2 $240.52   5.424%   $253.5658   $253.57   $253.55   $253.60  
  Purchase #3 $105.33   6.388%   $112.0585   $112.06   $112.05   $112.10  
  Purchase #4 $142.80   7.156%   $153.0188   $153.02   $153.00   $153.00  
  Purchase #5 $145.72   9.179%   $159.0956   $159.10   $159.10   $159.10  
  Purchase #6 $54.56   8.542%   $59.2205   $59.22   $59.20   $59.20  
  Purchase #7 $24.41   7.268%   $26.1841   $26.18   $26.20   $26.20  
  7 purchase totals = $913.84       $975.0497   $975.06   $975.00   $975.10