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 $197.41   3.480%   $204.2799   $204.28   $204.30   $204.30  
  Purchase #2 $225.39   3.605%   $233.5153   $233.52   $233.50   $233.50  
  Purchase #3 $152.83   5.690%   $161.526   $161.53   $161.55   $161.50  
  Purchase #4 $219.39   10.592%   $242.6278   $242.63   $242.65   $242.60  
  Purchase #5 $97.82   8.363%   $106.0007   $106.00   $106.00   $106.00  
  Purchase #6 $64.26   6.369%   $68.3527   $68.35   $68.35   $68.40  
  Purchase #7 $190.84   4.814%   $200.027   $200.03   $200.05   $200.00  
  7 purchase totals = $1,147.94       $1,216.3294   $1,216.34   $1,216.40   $1,216.30