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 $71.76   6.164%   $76.1833   $76.18   $76.20   $76.20  
  Purchase #2 $209.30   7.809%   $225.6442   $225.64   $225.65   $225.60  
  Purchase #3 $15.95   3.245%   $16.4676   $16.47   $16.45   $16.50  
  Purchase #4 $131.29   9.524%   $143.7941   $143.79   $143.80   $143.80  
  Purchase #5 $203.68   4.531%   $212.9087   $212.91   $212.90   $212.90  
  Purchase #6 $201.69   10.265%   $222.3935   $222.39   $222.40   $222.40  
  Purchase #7 $236.89   11.355%   $263.7889   $263.79   $263.80   $263.80  
  7 purchase totals = $1,070.56       $1,161.1803   $1,161.17   $1,161.20   $1,161.20