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 $64.68   5.378%   $68.1585   $68.16   $68.15   $68.20  
  Purchase #2 $198.44   12.319%   $222.8858   $222.89   $222.90   $222.90  
  Purchase #3 $159.54   5.432%   $168.2062   $168.21   $168.20   $168.20  
  Purchase #4 $82.96   5.384%   $87.4266   $87.43   $87.45   $87.40  
  Purchase #5 $196.26   9.751%   $215.3973   $215.40   $215.40   $215.40  
  Purchase #6 $118.31   11.508%   $131.9251   $131.93   $131.95   $131.90  
  Purchase #7 $221.80   8.827%   $241.3783   $241.38   $241.40   $241.40  
  7 purchase totals = $1,041.99       $1,135.3778   $1,135.40   $1,135.45   $1,135.40