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 $12.34   7.660%   $13.2852   $13.29   $13.30   $13.30  
  Purchase #2 $74.59   4.225%   $77.7414   $77.74   $77.75   $77.70  
  Purchase #3 $213.99   5.161%   $225.034   $225.03   $225.05   $225.00  
  Purchase #4 $26.41   6.140%   $28.0316   $28.03   $28.05   $28.00  
  Purchase #5 $77.50   8.551%   $84.127   $84.13   $84.15   $84.10  
  Purchase #6 $49.97   8.773%   $54.3539   $54.35   $54.35   $54.40  
  Purchase #7 $247.48   11.665%   $276.3485   $276.35   $276.35   $276.30  
  7 purchase totals = $702.28       $758.9216   $758.92   $759.00   $758.80