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 $246.59   6.611%   $262.8921   $262.89   $262.90   $262.90  
  Purchase #2 $164.38   12.202%   $184.4376   $184.44   $184.45   $184.40  
  Purchase #3 $213.40   9.303%   $233.2526   $233.25   $233.25   $233.30  
  Purchase #4 $141.63   3.301%   $146.3052   $146.31   $146.30   $146.30  
  Purchase #5 $191.95   6.255%   $203.9565   $203.96   $203.95   $204.00  
  Purchase #6 $25.92   9.285%   $28.3267   $28.33   $28.35   $28.30  
  Purchase #7 $111.38   13.869%   $126.8273   $126.83   $126.85   $126.80  
  7 purchase totals = $1,095.25       $1,185.9980   $1,186.01   $1,186.05   $1,186.00