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 $245.55   11.437%   $273.6336   $273.63   $273.65   $273.60  
  Purchase #2 $92.28   10.659%   $102.1161   $102.12   $102.10   $102.10  
  Purchase #3 $150.57   12.220%   $168.9697   $168.97   $168.95   $169.00  
  Purchase #4 $185.97   7.838%   $200.5463   $200.55   $200.55   $200.50  
  Purchase #5 $233.41   3.282%   $241.0705   $241.07   $241.05   $241.10  
  Purchase #6 $6.30   11.241%   $7.0082   $7.01   $7.00   $7.00  
  Purchase #7 $22.37   11.611%   $24.9674   $24.97   $24.95   $25.00  
  7 purchase totals = $936.45       $1,018.3118   $1,018.32   $1,018.25   $1,018.30