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 $59.93   11.763%   $66.9796   $66.98   $67.00   $67.00  
  Purchase #2 $160.94   10.541%   $177.9047   $177.90   $177.90   $177.90  
  Purchase #3 $153.72   9.503%   $168.328   $168.33   $168.35   $168.30  
  Purchase #4 $230.44   7.316%   $247.299   $247.30   $247.30   $247.30  
  Purchase #5 $135.89   10.131%   $149.657   $149.66   $149.65   $149.70  
  Purchase #6 $161.74   7.736%   $174.2522   $174.25   $174.25   $174.30  
  Purchase #7 $26.74   11.755%   $29.8833   $29.88   $29.90   $29.90  
  7 purchase totals = $929.40       $1,014.3038   $1,014.30   $1,014.35   $1,014.40