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 $233.52   13.338%   $264.6669   $264.67   $264.65   $264.70  
  Purchase #2 $204.62   9.562%   $224.1858   $224.19   $224.20   $224.20  
  Purchase #3 $45.78   8.267%   $49.5646   $49.56   $49.55   $49.60  
  Purchase #4 $104.49   10.160%   $115.1062   $115.11   $115.10   $115.10  
  Purchase #5 $115.98   7.160%   $124.2842   $124.28   $124.30   $124.30  
  Purchase #6 $148.86   6.573%   $158.6446   $158.64   $158.65   $158.60  
  Purchase #7 $240.26   8.268%   $260.1247   $260.12   $260.10   $260.10  
  7 purchase totals = $1,093.51       $1,196.5770   $1,196.57   $1,196.55   $1,196.60