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 $214.52   10.502%   $237.0489   $237.05   $237.05   $237.00  
  Purchase #2 $13.74   11.868%   $15.3707   $15.37   $15.35   $15.40  
  Purchase #3 $162.38   6.524%   $172.9737   $172.97   $172.95   $173.00  
  Purchase #4 $194.73   4.168%   $202.8463   $202.85   $202.85   $202.80  
  Purchase #5 $181.42   10.240%   $199.9974   $200.00   $200.00   $200.00  
  Purchase #6 $29.28   6.776%   $31.264   $31.26   $31.25   $31.30  
  Purchase #7 $60.86   12.497%   $68.4657   $68.47   $68.45   $68.50  
  7 purchase totals = $856.93       $927.9667   $927.97   $927.90   $928.00