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 $64.97   4.266%   $67.7416   $67.74   $67.75   $67.70  
  Purchase #2 $176.84   13.825%   $201.2881   $201.29   $201.30   $201.30  
  Purchase #3 $212.69   4.208%   $221.64   $221.64   $221.65   $221.60  
  Purchase #4 $162.52   12.858%   $183.4168   $183.42   $183.40   $183.40  
  Purchase #5 $6.29   13.609%   $7.146   $7.15   $7.15   $7.10  
  Purchase #6 $224.74   3.132%   $231.7789   $231.78   $231.80   $231.80  
  Purchase #7 $34.91   6.537%   $37.1921   $37.19   $37.20   $37.20  
  7 purchase totals = $882.96       $950.2035   $950.21   $950.25   $950.10