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 $228.67   9.156%   $249.607   $249.61   $249.60   $249.60  
  Purchase #2 $61.61   9.593%   $67.5202   $67.52   $67.50   $67.50  
  Purchase #3 $63.73   10.427%   $70.3751   $70.38   $70.40   $70.40  
  Purchase #4 $21.86   10.464%   $24.1474   $24.15   $24.15   $24.10  
  Purchase #5 $240.47   5.377%   $253.4001   $253.40   $253.40   $253.40  
  Purchase #6 $211.37   9.640%   $231.7461   $231.75   $231.75   $231.70  
  Purchase #7 $53.31   5.778%   $56.3903   $56.39   $56.40   $56.40  
  7 purchase totals = $881.02       $953.1862   $953.20   $953.20   $953.10