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 $233.60   12.244%   $262.202   $262.20   $262.20   $262.20  
  Purchase #2 $62.67   4.169%   $65.2827   $65.28   $65.30   $65.30  
  Purchase #3 $187.77   9.459%   $205.5312   $205.53   $205.55   $205.50  
  Purchase #4 $91.25   8.454%   $98.9643   $98.96   $98.95   $99.00  
  Purchase #5 $89.51   13.577%   $101.6628   $101.66   $101.65   $101.70  
  Purchase #6 $100.25   3.658%   $103.9171   $103.92   $103.90   $103.90  
  Purchase #7 $203.36   8.281%   $220.2002   $220.20   $220.20   $220.20  
  7 purchase totals = $968.41       $1,057.7603   $1,057.75   $1,057.75   $1,057.80