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 $54.68   5.811%   $57.8575   $57.86   $57.85   $57.90  
  Purchase #2 $91.65   3.659%   $95.0035   $95.00   $95.00   $95.00  
  Purchase #3 $100.53   7.641%   $108.2115   $108.21   $108.20   $108.20  
  Purchase #4 $39.28   5.210%   $41.3265   $41.33   $41.35   $41.30  
  Purchase #5 $168.62   12.322%   $189.3974   $189.40   $189.40   $189.40  
  Purchase #6 $43.92   7.321%   $47.1354   $47.14   $47.15   $47.10  
  Purchase #7 $29.41   7.153%   $31.5137   $31.51   $31.50   $31.50  
  7 purchase totals = $528.09       $570.4455   $570.45   $570.45   $570.40