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 $206.32   7.406%   $221.6001   $221.60   $221.60   $221.60  
  Purchase #2 $246.74   6.634%   $263.1087   $263.11   $263.10   $263.10  
  Purchase #3 $30.76   8.645%   $33.4192   $33.42   $33.40   $33.40  
  Purchase #4 $145.69   10.210%   $160.5649   $160.56   $160.55   $160.60  
  Purchase #5 $136.93   9.323%   $149.696   $149.70   $149.70   $149.70  
  Purchase #6 $121.31   3.329%   $125.3484   $125.35   $125.35   $125.30  
  Purchase #7 $68.49   7.739%   $73.7904   $73.79   $73.80   $73.80  
  7 purchase totals = $956.24       $1,027.5277   $1,027.53   $1,027.50   $1,027.50