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 $153.83   9.751%   $168.83   $168.83   $168.85   $168.80  
  Purchase #2 $62.42   8.819%   $67.9248   $67.92   $67.90   $67.90  
  Purchase #3 $145.69   6.520%   $155.189   $155.19   $155.20   $155.20  
  Purchase #4 $237.68   10.528%   $262.703   $262.70   $262.70   $262.70  
  Purchase #5 $167.46   5.714%   $177.0287   $177.03   $177.05   $177.00  
  Purchase #6 $126.46   4.850%   $132.5933   $132.59   $132.60   $132.60  
  Purchase #7 $150.93   13.645%   $171.5244   $171.52   $171.50   $171.50  
  7 purchase totals = $1,044.47       $1,135.7932   $1,135.78   $1,135.80   $1,135.70