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 $54.43   8.113%   $58.8459   $58.85   $58.85   $58.80  
  Purchase #2 $87.66   9.837%   $96.2831   $96.28   $96.30   $96.30  
  Purchase #3 $29.33   13.299%   $33.2306   $33.23   $33.25   $33.20  
  Purchase #4 $142.89   5.357%   $150.5446   $150.54   $150.55   $150.50  
  Purchase #5 $138.77   13.278%   $157.1959   $157.20   $157.20   $157.20  
  Purchase #6 $35.53   11.407%   $39.5829   $39.58   $39.60   $39.60  
  Purchase #7 $249.83   7.603%   $268.8246   $268.82   $268.80   $268.80  
  7 purchase totals = $738.44       $804.5076   $804.50   $804.55   $804.40