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 $174.96   9.685%   $191.9049   $191.90   $191.90   $191.90  
  Purchase #2 $216.82   4.663%   $226.9303   $226.93   $226.95   $226.90  
  Purchase #3 $46.52   6.831%   $49.6978   $49.70   $49.70   $49.70  
  Purchase #4 $183.53   5.864%   $194.2922   $194.29   $194.30   $194.30  
  Purchase #5 $180.66   7.862%   $194.8635   $194.86   $194.85   $194.90  
  Purchase #6 $180.78   12.432%   $203.2546   $203.25   $203.25   $203.30  
  Purchase #7 $136.35   8.726%   $148.2479   $148.25   $148.25   $148.20  
  7 purchase totals = $1,119.62       $1,209.1912   $1,209.18   $1,209.20   $1,209.20