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 $62.36   3.485%   $64.5332   $64.53   $64.55   $64.50  
  Purchase #2 $54.51   13.761%   $62.0111   $62.01   $62.00   $62.00  
  Purchase #3 $135.93   7.620%   $146.2879   $146.29   $146.30   $146.30  
  Purchase #4 $228.57   3.105%   $235.6671   $235.67   $235.65   $235.70  
  Purchase #5 $237.80   13.672%   $270.312   $270.31   $270.30   $270.30  
  Purchase #6 $186.26   3.571%   $192.9113   $192.91   $192.90   $192.90  
  Purchase #7 $160.33   9.453%   $175.486   $175.49   $175.50   $175.50  
  7 purchase totals = $1,065.76       $1,147.2086   $1,147.21   $1,147.20   $1,147.20