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 $168.79   11.184%   $187.6675   $187.67   $187.65   $187.70  
  Purchase #2 $24.95   4.266%   $26.0144   $26.01   $26.00   $26.00  
  Purchase #3 $93.71   8.847%   $102.0005   $102.00   $102.00   $102.00  
  Purchase #4 $205.40   6.298%   $218.3361   $218.34   $218.35   $218.30  
  Purchase #5 $158.95   4.420%   $165.9756   $165.98   $166.00   $166.00  
  Purchase #6 $21.71   9.507%   $23.774   $23.77   $23.75   $23.80  
  Purchase #7 $215.65   5.173%   $226.8056   $226.81   $226.80   $226.80  
  7 purchase totals = $889.16       $950.5737   $950.58   $950.55   $950.60