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 $229.58   5.234%   $241.5962   $241.60   $241.60   $241.60  
  Purchase #2 $173.72   13.812%   $197.7142   $197.71   $197.70   $197.70  
  Purchase #3 $187.44   7.743%   $201.9535   $201.95   $201.95   $202.00  
  Purchase #4 $94.87   6.345%   $100.8895   $100.89   $100.90   $100.90  
  Purchase #5 $55.66   7.505%   $59.8373   $59.84   $59.85   $59.80  
  Purchase #6 $98.86   13.566%   $112.2713   $112.27   $112.25   $112.30  
  Purchase #7 $14.46   12.682%   $16.2938   $16.29   $16.30   $16.30  
  7 purchase totals = $854.59       $930.5558   $930.55   $930.55   $930.60