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 $195.47   8.232%   $211.5611   $211.56   $211.55   $211.60  
  Purchase #2 $158.75   9.322%   $173.5487   $173.55   $173.55   $173.50  
  Purchase #3 $75.34   5.767%   $79.6849   $79.68   $79.70   $79.70  
  Purchase #4 $99.43   5.212%   $104.6123   $104.61   $104.60   $104.60  
  Purchase #5 $198.44   11.674%   $221.6059   $221.61   $221.60   $221.60  
  Purchase #6 $124.55   11.405%   $138.7549   $138.75   $138.75   $138.80  
  Purchase #7 $145.88   9.123%   $159.1886   $159.19   $159.20   $159.20  
  7 purchase totals = $997.86       $1,088.9564   $1,088.95   $1,088.95   $1,089.00