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 $180.31   11.484%   $201.0168   $201.02   $201.00   $201.00  
  Purchase #2 $69.84   8.349%   $75.6709   $75.67   $75.65   $75.70  
  Purchase #3 $121.96   8.602%   $132.451   $132.45   $132.45   $132.50  
  Purchase #4 $178.89   5.254%   $188.2889   $188.29   $188.30   $188.30  
  Purchase #5 $51.70   7.722%   $55.6923   $55.69   $55.70   $55.70  
  Purchase #6 $248.53   7.858%   $268.0595   $268.06   $268.05   $268.10  
  Purchase #7 $163.79   4.217%   $170.697   $170.70   $170.70   $170.70  
  7 purchase totals = $1,015.02       $1,091.8764   $1,091.88   $1,091.85   $1,092.00