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 $60.67   13.810%   $69.0485   $69.05   $69.05   $69.00  
  Purchase #2 $199.87   11.638%   $223.1309   $223.13   $223.15   $223.10  
  Purchase #3 $101.61   12.114%   $113.919   $113.92   $113.90   $113.90  
  Purchase #4 $142.92   12.768%   $161.168   $161.17   $161.15   $161.20  
  Purchase #5 $13.97   7.151%   $14.969   $14.97   $14.95   $15.00  
  Purchase #6 $87.79   9.437%   $96.0747   $96.07   $96.05   $96.10  
  Purchase #7 $90.52   9.257%   $98.8994   $98.90   $98.90   $98.90  
  7 purchase totals = $697.35       $777.2095   $777.21   $777.15   $777.20