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 $56.27   10.170%   $61.9927   $61.99   $62.00   $62.00  
  Purchase #2 $84.49   4.757%   $88.5092   $88.51   $88.50   $88.50  
  Purchase #3 $139.65   8.408%   $151.3918   $151.39   $151.40   $151.40  
  Purchase #4 $224.47   12.219%   $251.898   $251.90   $251.90   $251.90  
  Purchase #5 $237.94   6.297%   $252.9231   $252.92   $252.90   $252.90  
  Purchase #6 $51.76   11.363%   $57.6415   $57.64   $57.65   $57.60  
  Purchase #7 $195.84   4.375%   $204.408   $204.41   $204.40   $204.40  
  7 purchase totals = $990.42       $1,068.7643   $1,068.76   $1,068.75   $1,068.70