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 $62.77   4.652%   $65.6901   $65.69   $65.70   $65.70  
  Purchase #2 $122.54   8.388%   $132.8187   $132.82   $132.80   $132.80  
  Purchase #3 $156.64   13.348%   $177.5483   $177.55   $177.55   $177.50  
  Purchase #4 $163.95   12.322%   $184.1519   $184.15   $184.15   $184.20  
  Purchase #5 $212.36   9.563%   $232.668   $232.67   $232.65   $232.70  
  Purchase #6 $29.26   9.782%   $32.1222   $32.12   $32.10   $32.10  
  Purchase #7 $110.53   13.830%   $125.8163   $125.82   $125.80   $125.80  
  7 purchase totals = $858.05       $950.8155   $950.82   $950.75   $950.80