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 $217.95   11.735%   $243.5264   $243.53   $243.55   $243.50  
  Purchase #2 $125.61   9.448%   $137.4776   $137.48   $137.50   $137.50  
  Purchase #3 $16.28   9.352%   $17.8025   $17.80   $17.80   $17.80  
  Purchase #4 $146.55   12.695%   $165.1545   $165.15   $165.15   $165.20  
  Purchase #5 $29.28   6.632%   $31.2218   $31.22   $31.20   $31.20  
  Purchase #6 $219.80   8.381%   $238.2214   $238.22   $238.20   $238.20  
  Purchase #7 $243.57   11.752%   $272.1943   $272.19   $272.20   $272.20  
  7 purchase totals = $999.04       $1,105.5985   $1,105.59   $1,105.60   $1,105.60