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 $24.43   5.303%   $25.7255   $25.73   $25.75   $25.70  
  Purchase #2 $29.63   4.854%   $31.0682   $31.07   $31.05   $31.10  
  Purchase #3 $75.66   5.724%   $79.9908   $79.99   $80.00   $80.00  
  Purchase #4 $56.92   5.489%   $60.0443   $60.04   $60.05   $60.00  
  Purchase #5 $187.78   7.456%   $201.7809   $201.78   $201.80   $201.80  
  Purchase #6 $91.78   4.381%   $95.8009   $95.80   $95.80   $95.80  
  Purchase #7 $101.57   5.138%   $106.7887   $106.79   $106.80   $106.80  
  7 purchase totals = $567.77       $601.1993   $601.20   $601.25   $601.20