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 $121.38   4.415%   $126.7389   $126.74   $126.75   $126.70  
  Purchase #2 $163.42   6.452%   $173.9639   $173.96   $173.95   $174.00  
  Purchase #3 $183.36   6.145%   $194.6275   $194.63   $194.65   $194.60  
  Purchase #4 $95.58   10.743%   $105.8482   $105.85   $105.85   $105.80  
  Purchase #5 $74.94   12.212%   $84.0917   $84.09   $84.10   $84.10  
  Purchase #6 $87.80   10.479%   $97.0006   $97.00   $97.00   $97.00  
  Purchase #7 $202.89   13.107%   $229.4828   $229.48   $229.50   $229.50  
  7 purchase totals = $929.37       $1,011.7536   $1,011.75   $1,011.80   $1,011.70