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 $71.39   4.436%   $74.5569   $74.56   $74.55   $74.60  
  Purchase #2 $34.48   4.300%   $35.9626   $35.96   $35.95   $36.00  
  Purchase #3 $18.84   7.274%   $20.2104   $20.21   $20.20   $20.20  
  Purchase #4 $68.77   8.135%   $74.3644   $74.36   $74.35   $74.40  
  Purchase #5 $153.31   9.150%   $167.3379   $167.34   $167.35   $167.30  
  Purchase #6 $206.42   8.236%   $223.4208   $223.42   $223.40   $223.40  
  Purchase #7 $144.68   12.765%   $163.1484   $163.15   $163.15   $163.10  
  7 purchase totals = $697.89       $759.0014   $759.00   $758.95   $759.00