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 $68.61   9.776%   $75.3173   $75.32   $75.30   $75.30  
  Purchase #2 $171.42   5.214%   $180.3578   $180.36   $180.35   $180.40  
  Purchase #3 $183.29   4.635%   $191.7855   $191.79   $191.80   $191.80  
  Purchase #4 $228.44   11.496%   $254.7015   $254.70   $254.70   $254.70  
  Purchase #5 $168.91   4.533%   $176.5667   $176.57   $176.55   $176.60  
  Purchase #6 $108.26   12.525%   $121.8196   $121.82   $121.80   $121.80  
  Purchase #7 $24.51   12.737%   $27.6318   $27.63   $27.65   $27.60  
  7 purchase totals = $953.44       $1,028.1802   $1,028.19   $1,028.15   $1,028.20