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 $83.98   8.694%   $91.2812   $91.28   $91.30   $91.30  
  Purchase #2 $190.96   12.756%   $215.3189   $215.32   $215.30   $215.30  
  Purchase #3 $157.94   3.462%   $163.4079   $163.41   $163.40   $163.40  
  Purchase #4 $238.43   8.864%   $259.5644   $259.56   $259.55   $259.60  
  Purchase #5 $108.37   5.231%   $114.0388   $114.04   $114.05   $114.00  
  Purchase #6 $35.99   10.300%   $39.697   $39.70   $39.70   $39.70  
  Purchase #7 $59.72   3.771%   $61.972   $61.97   $61.95   $62.00  
  7 purchase totals = $875.39       $945.2802   $945.28   $945.25   $945.30