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 $88.46   6.566%   $94.2683   $94.27   $94.25   $94.30  
  Purchase #2 $172.45   10.135%   $189.9278   $189.93   $189.95   $189.90  
  Purchase #3 $9.84   4.246%   $10.2578   $10.26   $10.25   $10.30  
  Purchase #4 $28.94   13.874%   $32.9551   $32.96   $32.95   $33.00  
  Purchase #5 $91.77   4.344%   $95.7565   $95.76   $95.75   $95.80  
  Purchase #6 $177.64   13.770%   $202.101   $202.10   $202.10   $202.10  
  Purchase #7 $229.57   13.691%   $261.0004   $261.00   $261.00   $261.00  
  7 purchase totals = $798.67       $886.2669   $886.28   $886.25   $886.40