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 $64.83   13.720%   $73.7247   $73.72   $73.70   $73.70  
  Purchase #2 $194.83   3.496%   $201.6413   $201.64   $201.65   $201.60  
  Purchase #3 $167.88   3.851%   $174.3451   $174.35   $174.35   $174.30  
  Purchase #4 $56.57   13.500%   $64.207   $64.21   $64.20   $64.20  
  Purchase #5 $41.88   6.665%   $44.6713   $44.67   $44.65   $44.70  
  Purchase #6 $230.53   13.301%   $261.1928   $261.19   $261.20   $261.20  
  Purchase #7 $142.55   12.508%   $160.3802   $160.38   $160.40   $160.40  
  7 purchase totals = $899.07       $980.1624   $980.16   $980.15   $980.10