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 $69.65   11.622%   $77.7447   $77.74   $77.75   $77.70  
  Purchase #2 $26.60   8.829%   $28.9485   $28.95   $28.95   $28.90  
  Purchase #3 $29.36   10.860%   $32.5485   $32.55   $32.55   $32.50  
  Purchase #4 $188.79   4.231%   $196.7777   $196.78   $196.80   $196.80  
  Purchase #5 $179.80   8.182%   $194.5112   $194.51   $194.50   $194.50  
  Purchase #6 $61.94   10.628%   $68.523   $68.52   $68.50   $68.50  
  Purchase #7 $149.87   9.236%   $163.712   $163.71   $163.70   $163.70  
  7 purchase totals = $706.01       $762.7656   $762.76   $762.75   $762.60