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 $196.74   12.455%   $221.244   $221.24   $221.25   $221.20  
  Purchase #2 $202.25   12.223%   $226.971   $226.97   $226.95   $227.00  
  Purchase #3 $181.28   11.283%   $201.7338   $201.73   $201.75   $201.70  
  Purchase #4 $99.77   10.281%   $110.0274   $110.03   $110.05   $110.00  
  Purchase #5 $11.96   11.528%   $13.3387   $13.34   $13.35   $13.30  
  Purchase #6 $246.96   8.116%   $267.0033   $267.00   $267.00   $267.00  
  Purchase #7 $155.84   11.535%   $173.8161   $173.82   $173.80   $173.80  
  7 purchase totals = $1,094.80       $1,214.1343   $1,214.13   $1,214.15   $1,214.00