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 $182.93   11.619%   $204.1846   $204.18   $204.20   $204.20  
  Purchase #2 $20.37   8.550%   $22.1116   $22.11   $22.10   $22.10  
  Purchase #3 $130.28   10.412%   $143.8448   $143.84   $143.85   $143.80  
  Purchase #4 $154.70   9.492%   $169.3841   $169.38   $169.40   $169.40  
  Purchase #5 $249.65   13.108%   $282.3741   $282.37   $282.35   $282.40  
  Purchase #6 $61.94   3.488%   $64.1005   $64.10   $64.10   $64.10  
  Purchase #7 $247.51   13.676%   $281.3595   $281.36   $281.35   $281.40  
  7 purchase totals = $1,047.38       $1,167.3592   $1,167.34   $1,167.35   $1,167.40