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 $89.68   7.706%   $96.5907   $96.59   $96.60   $96.60  
  Purchase #2 $118.82   6.208%   $126.1963   $126.20   $126.20   $126.20  
  Purchase #3 $133.65   4.190%   $139.2499   $139.25   $139.25   $139.20  
  Purchase #4 $209.36   5.332%   $220.5231   $220.52   $220.50   $220.50  
  Purchase #5 $189.40   9.275%   $206.9669   $206.97   $206.95   $207.00  
  Purchase #6 $107.26   3.131%   $110.6183   $110.62   $110.60   $110.60  
  Purchase #7 $141.54   9.344%   $154.7655   $154.77   $154.75   $154.80  
  7 purchase totals = $989.71       $1,054.9107   $1,054.92   $1,054.85   $1,054.90