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 $113.60   11.355%   $126.4993   $126.50   $126.50   $126.50  
  Purchase #2 $228.48   12.472%   $256.976   $256.98   $257.00   $257.00  
  Purchase #3 $38.45   9.793%   $42.2154   $42.22   $42.20   $42.20  
  Purchase #4 $119.29   6.434%   $126.9651   $126.97   $126.95   $127.00  
  Purchase #5 $207.74   9.139%   $226.7254   $226.73   $226.75   $226.70  
  Purchase #6 $167.38   8.734%   $181.999   $182.00   $182.00   $182.00  
  Purchase #7 $41.55   10.813%   $46.0428   $46.04   $46.05   $46.00  
  7 purchase totals = $916.49       $1,007.4230   $1,007.44   $1,007.45   $1,007.40