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 $7.75   7.550%   $8.3351   $8.34   $8.35   $8.30  
  Purchase #2 $189.95   11.806%   $212.3755   $212.38   $212.40   $212.40  
  Purchase #3 $47.33   11.247%   $52.6532   $52.65   $52.65   $52.70  
  Purchase #4 $11.79   12.166%   $13.2244   $13.22   $13.20   $13.20  
  Purchase #5 $115.51   4.173%   $120.3302   $120.33   $120.35   $120.30  
  Purchase #6 $36.90   7.788%   $39.7738   $39.77   $39.75   $39.80  
  Purchase #7 $106.43   6.536%   $113.3863   $113.39   $113.40   $113.40  
  7 purchase totals = $515.66       $560.0785   $560.08   $560.10   $560.10