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 $220.74   11.817%   $246.8248   $246.82   $246.80   $246.80  
  Purchase #2 $221.87   6.582%   $236.4735   $236.47   $236.45   $236.50  
  Purchase #3 $128.38   12.743%   $144.7395   $144.74   $144.75   $144.70  
  Purchase #4 $11.73   6.529%   $12.4959   $12.50   $12.50   $12.50  
  Purchase #5 $220.96   10.347%   $243.8227   $243.82   $243.80   $243.80  
  Purchase #6 $211.29   6.259%   $224.5146   $224.51   $224.50   $224.50  
  Purchase #7 $28.99   12.816%   $32.7054   $32.71   $32.70   $32.70  
  7 purchase totals = $1,043.96       $1,141.5764   $1,141.57   $1,141.50   $1,141.50