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 $49.34   5.606%   $52.106   $52.11   $52.10   $52.10  
  Purchase #2 $218.43   6.804%   $233.292   $233.29   $233.30   $233.30  
  Purchase #3 $195.77   12.777%   $220.7835   $220.78   $220.80   $220.80  
  Purchase #4 $92.33   5.496%   $97.4045   $97.40   $97.40   $97.40  
  Purchase #5 $135.55   13.668%   $154.077   $154.08   $154.10   $154.10  
  Purchase #6 $187.71   9.270%   $205.1107   $205.11   $205.10   $205.10  
  Purchase #7 $11.55   7.631%   $12.4314   $12.43   $12.45   $12.40  
  7 purchase totals = $890.68       $975.2051   $975.20   $975.25   $975.20