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 $246.62   4.203%   $256.9854   $256.99   $257.00   $257.00  
  Purchase #2 $195.81   4.476%   $204.5745   $204.57   $204.55   $204.60  
  Purchase #3 $177.80   3.385%   $183.8185   $183.82   $183.80   $183.80  
  Purchase #4 $230.29   11.754%   $257.3583   $257.36   $257.35   $257.40  
  Purchase #5 $195.64   5.562%   $206.5215   $206.52   $206.50   $206.50  
  Purchase #6 $200.71   11.355%   $223.5006   $223.50   $223.50   $223.50  
  Purchase #7 $96.79   6.377%   $102.9623   $102.96   $102.95   $103.00  
  7 purchase totals = $1,343.66       $1,435.7211   $1,435.72   $1,435.65   $1,435.80