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 $12.29   7.822%   $13.2513   $13.25   $13.25   $13.30  
  Purchase #2 $227.61   5.819%   $240.8546   $240.85   $240.85   $240.90  
  Purchase #3 $205.34   5.297%   $216.2169   $216.22   $216.20   $216.20  
  Purchase #4 $131.81   5.363%   $138.879   $138.88   $138.90   $138.90  
  Purchase #5 $167.58   8.652%   $182.079   $182.08   $182.10   $182.10  
  Purchase #6 $148.37   5.493%   $156.52   $156.52   $156.50   $156.50  
  Purchase #7 $230.94   10.192%   $254.4774   $254.48   $254.50   $254.50  
  7 purchase totals = $1,123.94       $1,202.2782   $1,202.28   $1,202.30   $1,202.40