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 $228.49   13.623%   $259.6172   $259.62   $259.60   $259.60  
  Purchase #2 $138.93   7.133%   $148.8399   $148.84   $148.85   $148.80  
  Purchase #3 $57.96   6.139%   $61.5182   $61.52   $61.50   $61.50  
  Purchase #4 $83.67   7.670%   $90.0875   $90.09   $90.10   $90.10  
  Purchase #5 $169.50   8.753%   $184.3363   $184.34   $184.35   $184.30  
  Purchase #6 $56.59   11.571%   $63.138   $63.14   $63.15   $63.10  
  Purchase #7 $221.33   10.715%   $245.0455   $245.05   $245.05   $245.00  
  7 purchase totals = $956.47       $1,052.5826   $1,052.60   $1,052.60   $1,052.40