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 $88.42   12.679%   $99.6308   $99.63   $99.65   $99.60  
  Purchase #2 $91.89   4.165%   $95.7172   $95.72   $95.70   $95.70  
  Purchase #3 $151.37   8.492%   $164.2243   $164.22   $164.20   $164.20  
  Purchase #4 $37.74   9.769%   $41.4268   $41.43   $41.45   $41.40  
  Purchase #5 $206.65   7.817%   $222.8038   $222.80   $222.80   $222.80  
  Purchase #6 $5.84   7.158%   $6.258   $6.26   $6.25   $6.30  
  Purchase #7 $114.30   5.403%   $120.4756   $120.48   $120.50   $120.50  
  7 purchase totals = $696.21       $750.5365   $750.54   $750.55   $750.50