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 $224.90   11.838%   $251.5237   $251.52   $251.50   $251.50  
  Purchase #2 $192.34   9.567%   $210.7412   $210.74   $210.75   $210.70  
  Purchase #3 $173.42   5.226%   $182.4829   $182.48   $182.50   $182.50  
  Purchase #4 $151.95   8.779%   $165.2897   $165.29   $165.30   $165.30  
  Purchase #5 $111.75   7.404%   $120.024   $120.02   $120.00   $120.00  
  Purchase #6 $24.34   9.185%   $26.5756   $26.58   $26.60   $26.60  
  Purchase #7 $108.79   8.445%   $117.9773   $117.98   $118.00   $118.00  
  7 purchase totals = $987.49       $1,074.6144   $1,074.61   $1,074.65   $1,074.60