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 $244.93   6.140%   $259.9687   $259.97   $259.95   $260.00  
  Purchase #2 $52.33   4.727%   $54.8036   $54.80   $54.80   $54.80  
  Purchase #3 $87.77   11.814%   $98.1391   $98.14   $98.15   $98.10  
  Purchase #4 $206.56   8.437%   $223.9875   $223.99   $224.00   $224.00  
  Purchase #5 $84.55   6.526%   $90.0677   $90.07   $90.05   $90.10  
  Purchase #6 $56.57   8.179%   $61.1969   $61.20   $61.20   $61.20  
  Purchase #7 $246.94   7.487%   $265.4284   $265.43   $265.45   $265.40  
  7 purchase totals = $979.65       $1,053.5919   $1,053.60   $1,053.60   $1,053.60