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 $57.31   8.496%   $62.1791   $62.18   $62.20   $62.20  
  Purchase #2 $249.49   12.847%   $281.542   $281.54   $281.55   $281.50  
  Purchase #3 $211.53   10.131%   $232.9601   $232.96   $232.95   $233.00  
  Purchase #4 $236.92   13.783%   $269.5747   $269.57   $269.55   $269.60  
  Purchase #5 $244.76   3.390%   $253.0574   $253.06   $253.05   $253.10  
  Purchase #6 $185.43   6.426%   $197.3457   $197.35   $197.35   $197.30  
  Purchase #7 $158.56   6.871%   $169.4547   $169.45   $169.45   $169.50  
  7 purchase totals = $1,344.00       $1,466.1137   $1,466.11   $1,466.10   $1,466.20