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 $47.26   6.198%   $50.1892   $50.19   $50.20   $50.20  
  Purchase #2 $169.84   11.794%   $189.8709   $189.87   $189.85   $189.90  
  Purchase #3 $233.46   13.467%   $264.9001   $264.90   $264.90   $264.90  
  Purchase #4 $246.50   13.167%   $278.9567   $278.96   $278.95   $279.00  
  Purchase #5 $96.28   11.551%   $107.4013   $107.40   $107.40   $107.40  
  Purchase #6 $39.70   13.449%   $45.0393   $45.04   $45.05   $45.00  
  Purchase #7 $74.63   5.133%   $78.4608   $78.46   $78.45   $78.50  
  7 purchase totals = $907.67       $1,014.8183   $1,014.82   $1,014.80   $1,014.90