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 $231.53   8.721%   $251.7217   $251.72   $251.70   $251.70  
  Purchase #2 $30.32   3.678%   $31.4352   $31.44   $31.45   $31.40  
  Purchase #3 $80.42   9.549%   $88.0993   $88.10   $88.10   $88.10  
  Purchase #4 $137.86   5.447%   $145.3692   $145.37   $145.35   $145.40  
  Purchase #5 $222.47   3.322%   $229.8605   $229.86   $229.85   $229.90  
  Purchase #6 $68.38   12.396%   $76.8564   $76.86   $76.85   $76.90  
  Purchase #7 $187.90   6.546%   $200.1999   $200.20   $200.20   $200.20  
  7 purchase totals = $958.88       $1,023.5422   $1,023.55   $1,023.50   $1,023.60