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 $203.53   11.133%   $226.189   $226.19   $226.20   $226.20  
  Purchase #2 $147.58   6.425%   $157.062   $157.06   $157.05   $157.10  
  Purchase #3 $54.73   11.691%   $61.1285   $61.13   $61.15   $61.10  
  Purchase #4 $245.30   12.197%   $275.2192   $275.22   $275.20   $275.20  
  Purchase #5 $31.97   10.139%   $35.2114   $35.21   $35.20   $35.20  
  Purchase #6 $195.82   12.268%   $219.8432   $219.84   $219.85   $219.80  
  Purchase #7 $50.76   5.252%   $53.4259   $53.43   $53.45   $53.40  
  7 purchase totals = $929.69       $1,028.0792   $1,028.08   $1,028.10   $1,028.00