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 $87.67   6.489%   $93.3589   $93.36   $93.35   $93.40  
  Purchase #2 $35.54   6.179%   $37.736   $37.74   $37.75   $37.70  
  Purchase #3 $230.25   5.551%   $243.0312   $243.03   $243.05   $243.00  
  Purchase #4 $101.73   11.140%   $113.0627   $113.06   $113.05   $113.10  
  Purchase #5 $194.92   5.537%   $205.7127   $205.71   $205.70   $205.70  
  Purchase #6 $44.45   7.438%   $47.7562   $47.76   $47.75   $47.80  
  Purchase #7 $52.32   6.228%   $55.5785   $55.58   $55.60   $55.60  
  7 purchase totals = $746.88       $796.2362   $796.24   $796.25   $796.30