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 $87.65   5.626%   $92.5812   $92.58   $92.60   $92.60  
  Purchase #2 $128.58   3.167%   $132.6521   $132.65   $132.65   $132.70  
  Purchase #3 $235.35   4.767%   $246.5691   $246.57   $246.55   $246.60  
  Purchase #4 $41.73   3.617%   $43.2394   $43.24   $43.25   $43.20  
  Purchase #5 $28.31   11.529%   $31.5739   $31.57   $31.55   $31.60  
  Purchase #6 $209.83   5.760%   $221.9162   $221.92   $221.90   $221.90  
  Purchase #7 $68.57   7.529%   $73.7326   $73.73   $73.75   $73.70  
  7 purchase totals = $800.02       $842.2645   $842.26   $842.25   $842.30