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 $232.94   9.330%   $254.6733   $254.67   $254.65   $254.70  
  Purchase #2 $156.28   4.609%   $163.4829   $163.48   $163.50   $163.50  
  Purchase #3 $77.98   7.648%   $83.9439   $83.94   $83.95   $83.90  
  Purchase #4 $219.54   12.174%   $246.2668   $246.27   $246.25   $246.30  
  Purchase #5 $66.51   3.406%   $68.7753   $68.78   $68.80   $68.80  
  Purchase #6 $165.40   7.833%   $178.3558   $178.36   $178.35   $178.40  
  Purchase #7 $46.83   5.374%   $49.3466   $49.35   $49.35   $49.30  
  7 purchase totals = $965.48       $1,044.8446   $1,044.85   $1,044.85   $1,044.90