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 $197.56   3.240%   $203.9609   $203.96   $203.95   $204.00  
  Purchase #2 $56.98   7.444%   $61.2216   $61.22   $61.20   $61.20  
  Purchase #3 $243.92   13.855%   $277.7151   $277.72   $277.70   $277.70  
  Purchase #4 $16.90   10.154%   $18.616   $18.62   $18.60   $18.60  
  Purchase #5 $89.43   4.502%   $93.4561   $93.46   $93.45   $93.50  
  Purchase #6 $12.37   12.641%   $13.9337   $13.93   $13.95   $13.90  
  Purchase #7 $229.51   10.356%   $253.2781   $253.28   $253.30   $253.30  
  7 purchase totals = $846.67       $922.1815   $922.19   $922.15   $922.20