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 $218.37   11.162%   $242.7445   $242.74   $242.75   $242.70  
  Purchase #2 $73.82   11.120%   $82.0288   $82.03   $82.05   $82.00  
  Purchase #3 $238.63   12.358%   $268.1199   $268.12   $268.10   $268.10  
  Purchase #4 $187.26   4.778%   $196.2073   $196.21   $196.20   $196.20  
  Purchase #5 $85.82   3.110%   $88.489   $88.49   $88.50   $88.50  
  Purchase #6 $136.90   6.609%   $145.9477   $145.95   $145.95   $145.90  
  Purchase #7 $167.31   11.236%   $186.109   $186.11   $186.10   $186.10  
  7 purchase totals = $1,108.11       $1,209.6462   $1,209.65   $1,209.65   $1,209.50