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 $54.63   13.545%   $62.0296   $62.03   $62.05   $62.00  
  Purchase #2 $79.87   11.363%   $88.9456   $88.95   $88.95   $88.90  
  Purchase #3 $121.96   12.654%   $137.3928   $137.39   $137.40   $137.40  
  Purchase #4 $233.79   6.499%   $248.984   $248.98   $249.00   $249.00  
  Purchase #5 $144.86   13.846%   $164.9173   $164.92   $164.90   $164.90  
  Purchase #6 $162.44   13.333%   $184.0981   $184.10   $184.10   $184.10  
  Purchase #7 $195.54   4.364%   $204.0734   $204.07   $204.05   $204.10  
  7 purchase totals = $993.09       $1,090.4408   $1,090.44   $1,090.45   $1,090.40