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 $52.48   11.192%   $58.3536   $58.35   $58.35   $58.40  
  Purchase #2 $97.63   11.786%   $109.1367   $109.14   $109.15   $109.10  
  Purchase #3 $62.57   13.458%   $70.9907   $70.99   $71.00   $71.00  
  Purchase #4 $36.63   6.498%   $39.0102   $39.01   $39.00   $39.00  
  Purchase #5 $111.33   4.471%   $116.3076   $116.31   $116.30   $116.30  
  Purchase #6 $167.37   9.169%   $182.7162   $182.72   $182.70   $182.70  
  Purchase #7 $231.31   13.457%   $262.4374   $262.44   $262.45   $262.40  
  7 purchase totals = $759.32       $838.9524   $838.96   $838.95   $838.90