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 $55.31   13.710%   $62.893   $62.89   $62.90   $62.90  
  Purchase #2 $153.97   7.801%   $165.9812   $165.98   $166.00   $166.00  
  Purchase #3 $116.96   6.549%   $124.6197   $124.62   $124.60   $124.60  
  Purchase #4 $213.43   6.145%   $226.5453   $226.55   $226.55   $226.50  
  Purchase #5 $103.71   6.315%   $110.2593   $110.26   $110.25   $110.30  
  Purchase #6 $139.29   9.364%   $152.3331   $152.33   $152.35   $152.30  
  Purchase #7 $130.74   8.592%   $141.9732   $141.97   $141.95   $142.00  
  7 purchase totals = $913.41       $984.6048   $984.60   $984.60   $984.60