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 $91.44   6.261%   $97.1651   $97.17   $97.15   $97.20  
  Purchase #2 $241.84   5.442%   $255.0009   $255.00   $255.00   $255.00  
  Purchase #3 $245.62   11.546%   $273.9793   $273.98   $274.00   $274.00  
  Purchase #4 $198.43   9.746%   $217.769   $217.77   $217.75   $217.80  
  Purchase #5 $75.34   12.433%   $84.707   $84.71   $84.70   $84.70  
  Purchase #6 $56.59   6.563%   $60.304   $60.30   $60.30   $60.30  
  Purchase #7 $116.96   6.343%   $124.3788   $124.38   $124.40   $124.40  
  7 purchase totals = $1,026.22       $1,113.3041   $1,113.31   $1,113.30   $1,113.40