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 $83.79   8.612%   $91.006   $91.01   $91.00   $91.00  
  Purchase #2 $141.80   4.190%   $147.7414   $147.74   $147.75   $147.70  
  Purchase #3 $30.42   8.443%   $32.9884   $32.99   $33.00   $33.00  
  Purchase #4 $78.88   8.596%   $85.6605   $85.66   $85.65   $85.70  
  Purchase #5 $53.26   7.574%   $57.2939   $57.29   $57.30   $57.30  
  Purchase #6 $142.80   11.687%   $159.489   $159.49   $159.50   $159.50  
  Purchase #7 $247.47   4.186%   $257.8291   $257.83   $257.85   $257.80  
  7 purchase totals = $778.42       $832.0083   $832.01   $832.05   $832.00