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 $30.94   11.428%   $34.4758   $34.48   $34.50   $34.50  
  Purchase #2 $170.61   12.108%   $191.2675   $191.27   $191.25   $191.30  
  Purchase #3 $39.42   12.248%   $44.2482   $44.25   $44.25   $44.20  
  Purchase #4 $59.96   4.414%   $62.6066   $62.61   $62.60   $62.60  
  Purchase #5 $23.25   8.396%   $25.2021   $25.20   $25.20   $25.20  
  Purchase #6 $212.70   3.199%   $219.5043   $219.50   $219.50   $219.50  
  Purchase #7 $41.74   13.227%   $47.2609   $47.26   $47.25   $47.30  
  7 purchase totals = $578.62       $624.5654   $624.57   $624.55   $624.60