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 $241.62   7.227%   $259.0819   $259.08   $259.10   $259.10  
  Purchase #2 $244.32   4.230%   $254.6547   $254.65   $254.65   $254.70  
  Purchase #3 $70.29   9.534%   $76.9914   $76.99   $77.00   $77.00  
  Purchase #4 $218.35   6.262%   $232.0231   $232.02   $232.00   $232.00  
  Purchase #5 $109.42   7.215%   $117.3147   $117.31   $117.30   $117.30  
  Purchase #6 $184.42   9.494%   $201.9288   $201.93   $201.95   $201.90  
  Purchase #7 $84.86   11.151%   $94.3227   $94.32   $94.30   $94.30  
  7 purchase totals = $1,153.28       $1,236.3173   $1,236.30   $1,236.30   $1,236.30