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 $202.36   11.797%   $226.2324   $226.23   $226.25   $226.20  
  Purchase #2 $94.65   8.633%   $102.8211   $102.82   $102.80   $102.80  
  Purchase #3 $178.44   10.852%   $197.8043   $197.80   $197.80   $197.80  
  Purchase #4 $103.84   4.642%   $108.6603   $108.66   $108.65   $108.70  
  Purchase #5 $124.75   10.766%   $138.1806   $138.18   $138.20   $138.20  
  Purchase #6 $158.28   11.167%   $175.9551   $175.96   $175.95   $176.00  
  Purchase #7 $104.74   13.811%   $119.2056   $119.21   $119.20   $119.20  
  7 purchase totals = $967.06       $1,068.8594   $1,068.86   $1,068.85   $1,068.90