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 $49.90   10.630%   $55.2044   $55.20   $55.20   $55.20  
  Purchase #2 $193.29   4.227%   $201.4604   $201.46   $201.45   $201.50  
  Purchase #3 $158.39   5.419%   $166.9732   $166.97   $166.95   $167.00  
  Purchase #4 $39.48   11.137%   $43.8769   $43.88   $43.90   $43.90  
  Purchase #5 $64.60   9.325%   $70.624   $70.62   $70.60   $70.60  
  Purchase #6 $243.49   12.333%   $273.5196   $273.52   $273.50   $273.50  
  Purchase #7 $241.46   10.532%   $266.8906   $266.89   $266.90   $266.90  
  7 purchase totals = $990.61       $1,078.5491   $1,078.54   $1,078.50   $1,078.60