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 $196.85   3.404%   $203.5508   $203.55   $203.55   $203.60  
  Purchase #2 $239.58   9.370%   $262.0286   $262.03   $262.05   $262.00  
  Purchase #3 $86.43   12.387%   $97.1361   $97.14   $97.15   $97.10  
  Purchase #4 $190.25   7.378%   $204.2866   $204.29   $204.30   $204.30  
  Purchase #5 $230.55   9.206%   $251.7744   $251.77   $251.75   $251.80  
  Purchase #6 $232.28   8.317%   $251.5987   $251.60   $251.60   $251.60  
  Purchase #7 $237.25   11.819%   $265.2906   $265.29   $265.30   $265.30  
  7 purchase totals = $1,413.19       $1,535.6658   $1,535.67   $1,535.70   $1,535.70