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 $22.56   4.825%   $23.6485   $23.65   $23.65   $23.60  
  Purchase #2 $126.28   10.614%   $139.6834   $139.68   $139.70   $139.70  
  Purchase #3 $171.71   13.490%   $194.8737   $194.87   $194.85   $194.90  
  Purchase #4 $22.77   12.871%   $25.7007   $25.70   $25.70   $25.70  
  Purchase #5 $170.53   13.178%   $193.0024   $193.00   $193.00   $193.00  
  Purchase #6 $229.53   6.212%   $243.7884   $243.79   $243.80   $243.80  
  Purchase #7 $207.38   8.507%   $225.0218   $225.02   $225.00   $225.00  
  7 purchase totals = $950.76       $1,045.7189   $1,045.71   $1,045.70   $1,045.70