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 $130.92   11.764%   $146.3214   $146.32   $146.30   $146.30  
  Purchase #2 $235.81   8.570%   $256.0189   $256.02   $256.00   $256.00  
  Purchase #3 $134.51   6.114%   $142.7339   $142.73   $142.75   $142.70  
  Purchase #4 $166.47   3.746%   $172.706   $172.71   $172.70   $172.70  
  Purchase #5 $139.36   6.287%   $148.1216   $148.12   $148.10   $148.10  
  Purchase #6 $182.88   8.786%   $198.9478   $198.95   $198.95   $198.90  
  Purchase #7 $79.53   9.594%   $87.1601   $87.16   $87.15   $87.20  
  7 purchase totals = $1,069.48       $1,152.0097   $1,152.01   $1,151.95   $1,151.90