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 $196.27   8.759%   $213.4613   $213.46   $213.45   $213.50  
  Purchase #2 $190.33   5.645%   $201.0741   $201.07   $201.05   $201.10  
  Purchase #3 $117.72   8.304%   $127.4955   $127.50   $127.50   $127.50  
  Purchase #4 $102.34   3.864%   $106.2944   $106.29   $106.30   $106.30  
  Purchase #5 $135.63   6.824%   $144.8854   $144.89   $144.90   $144.90  
  Purchase #6 $80.90   11.255%   $90.0053   $90.01   $90.00   $90.00  
  Purchase #7 $136.90   8.823%   $148.9787   $148.98   $149.00   $149.00  
  7 purchase totals = $960.09       $1,032.1947   $1,032.20   $1,032.20   $1,032.30