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 $86.86   13.183%   $98.3108   $98.31   $98.30   $98.30  
  Purchase #2 $190.89   11.147%   $212.1685   $212.17   $212.15   $212.20  
  Purchase #3 $201.51   4.713%   $211.0072   $211.01   $211.00   $211.00  
  Purchase #4 $141.46   13.247%   $160.1992   $160.20   $160.20   $160.20  
  Purchase #5 $181.87   7.383%   $195.2975   $195.30   $195.30   $195.30  
  Purchase #6 $177.62   4.772%   $186.096   $186.10   $186.10   $186.10  
  Purchase #7 $152.88   12.452%   $171.9166   $171.92   $171.90   $171.90  
  7 purchase totals = $1,133.09       $1,234.9958   $1,235.01   $1,234.95   $1,235.00