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 $83.91   9.260%   $91.6801   $91.68   $91.70   $91.70  
  Purchase #2 $84.96   12.586%   $95.6531   $95.65   $95.65   $95.70  
  Purchase #3 $118.41   12.407%   $133.1011   $133.10   $133.10   $133.10  
  Purchase #4 $106.68   11.547%   $118.9983   $119.00   $119.00   $119.00  
  Purchase #5 $199.43   11.216%   $221.7981   $221.80   $221.80   $221.80  
  Purchase #6 $10.66   12.224%   $11.9631   $11.96   $11.95   $12.00  
  Purchase #7 $73.43   4.855%   $76.995   $77.00   $77.00   $77.00  
  7 purchase totals = $677.48       $750.1888   $750.19   $750.20   $750.30