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 $52.33   13.179%   $59.2266   $59.23   $59.25   $59.20  
  Purchase #2 $45.55   5.819%   $48.2006   $48.20   $48.20   $48.20  
  Purchase #3 $10.68   5.723%   $11.2912   $11.29   $11.30   $11.30  
  Purchase #4 $187.80   11.582%   $209.551   $209.55   $209.55   $209.60  
  Purchase #5 $206.58   6.190%   $219.3673   $219.37   $219.35   $219.40  
  Purchase #6 $198.86   12.779%   $224.2723   $224.27   $224.25   $224.30  
  Purchase #7 $180.44   13.388%   $204.5973   $204.60   $204.60   $204.60  
  7 purchase totals = $882.24       $976.5063   $976.51   $976.50   $976.60