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 $23.47   4.171%   $24.4489   $24.45   $24.45   $24.40  
  Purchase #2 $131.29   12.581%   $147.8076   $147.81   $147.80   $147.80  
  Purchase #3 $149.29   12.306%   $167.6616   $167.66   $167.65   $167.70  
  Purchase #4 $188.39   7.615%   $202.7359   $202.74   $202.75   $202.70  
  Purchase #5 $143.87   5.625%   $151.9627   $151.96   $151.95   $152.00  
  Purchase #6 $241.84   9.785%   $265.504   $265.50   $265.50   $265.50  
  Purchase #7 $109.69   5.307%   $115.5112   $115.51   $115.50   $115.50  
  7 purchase totals = $987.84       $1,075.6319   $1,075.63   $1,075.60   $1,075.60