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 $203.67   8.153%   $220.2752   $220.28   $220.30   $220.30  
  Purchase #2 $63.94   13.604%   $72.6384   $72.64   $72.65   $72.60  
  Purchase #3 $58.27   13.506%   $66.1399   $66.14   $66.15   $66.10  
  Purchase #4 $237.34   7.320%   $254.7133   $254.71   $254.70   $254.70  
  Purchase #5 $49.33   13.599%   $56.0384   $56.04   $56.05   $56.00  
  Purchase #6 $229.47   4.800%   $240.4846   $240.48   $240.50   $240.50  
  Purchase #7 $116.42   4.143%   $121.2433   $121.24   $121.25   $121.20  
  7 purchase totals = $958.44       $1,031.5331   $1,031.53   $1,031.60   $1,031.40