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 $63.79   10.794%   $70.6755   $70.68   $70.70   $70.70  
  Purchase #2 $98.51   5.283%   $103.7143   $103.71   $103.70   $103.70  
  Purchase #3 $41.72   10.714%   $46.1899   $46.19   $46.20   $46.20  
  Purchase #4 $76.76   9.453%   $84.0161   $84.02   $84.00   $84.00  
  Purchase #5 $238.31   7.543%   $256.2857   $256.29   $256.30   $256.30  
  Purchase #6 $160.27   8.334%   $173.6269   $173.63   $173.65   $173.60  
  Purchase #7 $243.65   11.169%   $270.8633   $270.86   $270.85   $270.90  
  7 purchase totals = $923.01       $1,005.3717   $1,005.38   $1,005.40   $1,005.40