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 $234.33   5.277%   $246.6956   $246.70   $246.70   $246.70  
  Purchase #2 $229.83   11.395%   $256.0191   $256.02   $256.00   $256.00  
  Purchase #3 $77.38   7.184%   $82.939   $82.94   $82.95   $82.90  
  Purchase #4 $38.95   12.107%   $43.6657   $43.67   $43.65   $43.70  
  Purchase #5 $243.93   5.548%   $257.4632   $257.46   $257.45   $257.50  
  Purchase #6 $67.41   5.582%   $71.1728   $71.17   $71.15   $71.20  
  Purchase #7 $159.48   4.855%   $167.2228   $167.22   $167.20   $167.20  
  7 purchase totals = $1,051.31       $1,125.1782   $1,125.18   $1,125.10   $1,125.20