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 $96.60   7.702%   $104.0401   $104.04   $104.05   $104.00  
  Purchase #2 $184.51   5.769%   $195.1544   $195.15   $195.15   $195.20  
  Purchase #3 $47.53   10.399%   $52.4726   $52.47   $52.45   $52.50  
  Purchase #4 $59.84   13.373%   $67.8424   $67.84   $67.85   $67.80  
  Purchase #5 $10.41   7.158%   $11.1551   $11.16   $11.15   $11.20  
  Purchase #6 $170.68   8.515%   $185.2134   $185.21   $185.20   $185.20  
  Purchase #7 $239.68   11.741%   $267.8208   $267.82   $267.80   $267.80  
  7 purchase totals = $809.25       $883.6988   $883.69   $883.65   $883.70