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 $57.48   9.186%   $62.7601   $62.76   $62.75   $62.80  
  Purchase #2 $22.74   9.681%   $24.9415   $24.94   $24.95   $24.90  
  Purchase #3 $213.37   7.844%   $230.1067   $230.11   $230.10   $230.10  
  Purchase #4 $33.35   4.607%   $34.8864   $34.89   $34.90   $34.90  
  Purchase #5 $101.91   6.332%   $108.3629   $108.36   $108.35   $108.40  
  Purchase #6 $71.84   11.661%   $80.2173   $80.22   $80.20   $80.20  
  Purchase #7 $229.75   10.158%   $253.088   $253.09   $253.10   $253.10  
  7 purchase totals = $730.44       $794.3629   $794.37   $794.35   $794.40