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 $86.46   8.209%   $93.5575   $93.56   $93.55   $93.60  
  Purchase #2 $176.89   7.109%   $189.4651   $189.47   $189.45   $189.50  
  Purchase #3 $67.52   6.803%   $72.1134   $72.11   $72.10   $72.10  
  Purchase #4 $58.72   9.579%   $64.3448   $64.34   $64.35   $64.30  
  Purchase #5 $206.43   5.734%   $218.2667   $218.27   $218.25   $218.30  
  Purchase #6 $164.35   11.322%   $182.9577   $182.96   $182.95   $183.00  
  Purchase #7 $205.30   11.400%   $228.7042   $228.70   $228.70   $228.70  
  7 purchase totals = $965.67       $1,049.4094   $1,049.41   $1,049.35   $1,049.50