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 $167.56   11.622%   $187.0338   $187.03   $187.05   $187.00  
  Purchase #2 $166.36   12.243%   $186.7275   $186.73   $186.75   $186.70  
  Purchase #3 $163.75   4.159%   $170.5604   $170.56   $170.55   $170.60  
  Purchase #4 $88.93   10.773%   $98.5104   $98.51   $98.50   $98.50  
  Purchase #5 $119.32   3.489%   $123.4831   $123.48   $123.50   $123.50  
  Purchase #6 $191.29   11.341%   $212.9842   $212.98   $213.00   $213.00  
  Purchase #7 $41.27   9.375%   $45.1391   $45.14   $45.15   $45.10  
  7 purchase totals = $938.48       $1,024.4385   $1,024.43   $1,024.50   $1,024.40