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 $189.65   8.285%   $205.3625   $205.36   $205.35   $205.40  
  Purchase #2 $41.67   4.782%   $43.6627   $43.66   $43.65   $43.70  
  Purchase #3 $233.46   11.789%   $260.9826   $260.98   $261.00   $261.00  
  Purchase #4 $210.49   8.490%   $228.3606   $228.36   $228.35   $228.40  
  Purchase #5 $184.81   13.338%   $209.46   $209.46   $209.45   $209.50  
  Purchase #6 $94.62   10.855%   $104.891   $104.89   $104.90   $104.90  
  Purchase #7 $133.66   8.126%   $144.5212   $144.52   $144.50   $144.50  
  7 purchase totals = $1,088.36       $1,197.2406   $1,197.23   $1,197.20   $1,197.40