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 $246.56   3.352%   $254.8247   $254.82   $254.80   $254.80  
  Purchase #2 $37.29   4.763%   $39.0661   $39.07   $39.05   $39.10  
  Purchase #3 $5.56   6.812%   $5.9387   $5.94   $5.95   $5.90  
  Purchase #4 $234.51   11.519%   $261.5232   $261.52   $261.50   $261.50  
  Purchase #5 $219.31   3.252%   $226.442   $226.44   $226.45   $226.40  
  Purchase #6 $58.76   9.161%   $64.143   $64.14   $64.15   $64.10  
  Purchase #7 $203.84   4.688%   $213.396   $213.40   $213.40   $213.40  
  7 purchase totals = $1,005.83       $1,065.3337   $1,065.33   $1,065.30   $1,065.20