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 $187.68   12.846%   $211.7894   $211.79   $211.80   $211.80  
  Purchase #2 $86.97   8.530%   $94.3885   $94.39   $94.40   $94.40  
  Purchase #3 $113.95   13.422%   $129.2444   $129.24   $129.25   $129.20  
  Purchase #4 $96.97   5.492%   $102.2956   $102.30   $102.30   $102.30  
  Purchase #5 $221.70   9.143%   $241.97   $241.97   $241.95   $242.00  
  Purchase #6 $143.93   3.147%   $148.4595   $148.46   $148.45   $148.50  
  Purchase #7 $88.67   10.663%   $98.1249   $98.12   $98.10   $98.10  
  7 purchase totals = $939.87       $1,026.2723   $1,026.27   $1,026.25   $1,026.30