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 $238.90   6.513%   $254.4596   $254.46   $254.45   $254.50  
  Purchase #2 $110.59   9.109%   $120.6636   $120.66   $120.65   $120.70  
  Purchase #3 $62.40   7.368%   $66.9976   $67.00   $67.00   $67.00  
  Purchase #4 $182.58   13.700%   $207.5935   $207.59   $207.60   $207.60  
  Purchase #5 $186.68   12.849%   $210.6665   $210.67   $210.65   $210.70  
  Purchase #6 $122.76   3.694%   $127.2948   $127.29   $127.30   $127.30  
  Purchase #7 $41.79   10.771%   $46.2912   $46.29   $46.30   $46.30  
  7 purchase totals = $945.70       $1,033.9668   $1,033.96   $1,033.95   $1,034.10