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 $47.84   11.212%   $53.2038   $53.20   $53.20   $53.20  
  Purchase #2 $212.27   5.218%   $223.3462   $223.35   $223.35   $223.30  
  Purchase #3 $240.90   9.486%   $263.7518   $263.75   $263.75   $263.80  
  Purchase #4 $249.25   9.363%   $272.5873   $272.59   $272.60   $272.60  
  Purchase #5 $122.44   7.756%   $131.9364   $131.94   $131.95   $131.90  
  Purchase #6 $162.91   13.307%   $184.5884   $184.59   $184.60   $184.60  
  Purchase #7 $243.30   5.348%   $256.3117   $256.31   $256.30   $256.30  
  7 purchase totals = $1,278.91       $1,385.7256   $1,385.73   $1,385.75   $1,385.70