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 $178.62   13.503%   $202.7391   $202.74   $202.75   $202.70  
  Purchase #2 $136.50   8.823%   $148.5434   $148.54   $148.55   $148.50  
  Purchase #3 $46.45   13.332%   $52.6427   $52.64   $52.65   $52.60  
  Purchase #4 $220.93   3.133%   $227.8517   $227.85   $227.85   $227.90  
  Purchase #5 $167.50   9.154%   $182.833   $182.83   $182.85   $182.80  
  Purchase #6 $169.74   8.531%   $184.2205   $184.22   $184.20   $184.20  
  Purchase #7 $107.37   12.626%   $120.9265   $120.93   $120.95   $120.90  
  7 purchase totals = $1,027.11       $1,119.7569   $1,119.75   $1,119.80   $1,119.60