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 $88.56   6.442%   $94.265   $94.27   $94.25   $94.30  
  Purchase #2 $119.92   9.641%   $131.4815   $131.48   $131.50   $131.50  
  Purchase #3 $35.85   7.387%   $38.4982   $38.50   $38.50   $38.50  
  Purchase #4 $142.43   3.465%   $147.3652   $147.37   $147.35   $147.40  
  Purchase #5 $192.66   6.260%   $204.7205   $204.72   $204.70   $204.70  
  Purchase #6 $212.68   10.299%   $234.5839   $234.58   $234.60   $234.60  
  Purchase #7 $68.48   11.785%   $76.5504   $76.55   $76.55   $76.60  
  7 purchase totals = $860.58       $927.4647   $927.47   $927.45   $927.60