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 $171.84   6.127%   $182.3686   $182.37   $182.35   $182.40  
  Purchase #2 $246.52   11.691%   $275.3407   $275.34   $275.35   $275.30  
  Purchase #3 $198.43   3.431%   $205.2381   $205.24   $205.25   $205.20  
  Purchase #4 $156.31   3.485%   $161.7574   $161.76   $161.75   $161.80  
  Purchase #5 $190.44   6.316%   $202.4682   $202.47   $202.45   $202.50  
  Purchase #6 $222.54   11.241%   $247.5557   $247.56   $247.55   $247.60  
  Purchase #7 $136.78   5.492%   $144.292   $144.29   $144.30   $144.30  
  7 purchase totals = $1,322.86       $1,419.0207   $1,419.03   $1,419.00   $1,419.10