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 $175.58   4.775%   $183.9639   $183.96   $183.95   $184.00  
  Purchase #2 $242.48   12.605%   $273.0446   $273.04   $273.05   $273.00  
  Purchase #3 $102.58   5.254%   $107.9696   $107.97   $107.95   $108.00  
  Purchase #4 $230.93   5.302%   $243.1739   $243.17   $243.15   $243.20  
  Purchase #5 $69.62   5.862%   $73.7011   $73.70   $73.70   $73.70  
  Purchase #6 $102.92   9.748%   $112.9526   $112.95   $112.95   $113.00  
  Purchase #7 $58.90   10.581%   $65.1322   $65.13   $65.15   $65.10  
  7 purchase totals = $983.01       $1,059.9379   $1,059.92   $1,059.90   $1,060.00