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 $152.61   4.713%   $159.8025   $159.80   $159.80   $159.80  
  Purchase #2 $204.29   7.817%   $220.2593   $220.26   $220.25   $220.30  
  Purchase #3 $62.65   13.589%   $71.1635   $71.16   $71.15   $71.20  
  Purchase #4 $155.91   3.781%   $161.805   $161.81   $161.80   $161.80  
  Purchase #5 $102.93   7.664%   $110.8186   $110.82   $110.80   $110.80  
  Purchase #6 $247.87   8.814%   $269.7173   $269.72   $269.70   $269.70  
  Purchase #7 $26.88   9.538%   $29.4438   $29.44   $29.45   $29.40  
  7 purchase totals = $953.14       $1,023.0100   $1,023.01   $1,022.95   $1,023.00