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 $172.33   12.373%   $193.6524   $193.65   $193.65   $193.70  
  Purchase #2 $152.71   13.562%   $173.4205   $173.42   $173.40   $173.40  
  Purchase #3 $234.30   11.431%   $261.0828   $261.08   $261.10   $261.10  
  Purchase #4 $246.98   7.226%   $264.8268   $264.83   $264.85   $264.80  
  Purchase #5 $213.58   10.119%   $235.1922   $235.19   $235.20   $235.20  
  Purchase #6 $74.84   10.565%   $82.7468   $82.75   $82.75   $82.70  
  Purchase #7 $35.53   3.250%   $36.6847   $36.68   $36.70   $36.70  
  7 purchase totals = $1,130.27       $1,247.6062   $1,247.60   $1,247.65   $1,247.60