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 $34.49   10.699%   $38.1801   $38.18   $38.20   $38.20  
  Purchase #2 $145.54   5.709%   $153.8489   $153.85   $153.85   $153.80  
  Purchase #3 $248.94   10.546%   $275.1932   $275.19   $275.20   $275.20  
  Purchase #4 $249.65   9.776%   $274.0558   $274.06   $274.05   $274.10  
  Purchase #5 $172.85   4.705%   $180.9826   $180.98   $181.00   $181.00  
  Purchase #6 $56.82   5.837%   $60.1366   $60.14   $60.15   $60.10  
  Purchase #7 $47.40   8.733%   $51.5394   $51.54   $51.55   $51.50  
  7 purchase totals = $955.69       $1,033.9366   $1,033.94   $1,034.00   $1,033.90