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 $65.66   11.547%   $73.2418   $73.24   $73.25   $73.20  
  Purchase #2 $62.55   10.841%   $69.331   $69.33   $69.35   $69.30  
  Purchase #3 $74.61   11.361%   $83.0864   $83.09   $83.10   $83.10  
  Purchase #4 $24.28   4.701%   $25.4214   $25.42   $25.40   $25.40  
  Purchase #5 $177.37   9.128%   $193.5603   $193.56   $193.55   $193.60  
  Purchase #6 $246.25   12.132%   $276.1251   $276.13   $276.15   $276.10  
  Purchase #7 $54.77   10.377%   $60.4535   $60.45   $60.45   $60.50  
  7 purchase totals = $705.49       $781.2195   $781.22   $781.25   $781.20