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 $246.85   5.588%   $260.644   $260.64   $260.65   $260.60  
  Purchase #2 $124.45   11.494%   $138.7543   $138.75   $138.75   $138.80  
  Purchase #3 $60.95   13.523%   $69.1923   $69.19   $69.20   $69.20  
  Purchase #4 $173.81   3.107%   $179.2103   $179.21   $179.20   $179.20  
  Purchase #5 $145.35   13.635%   $165.1685   $165.17   $165.15   $165.20  
  Purchase #6 $98.75   9.442%   $108.074   $108.07   $108.05   $108.10  
  Purchase #7 $79.47   4.455%   $83.0104   $83.01   $83.00   $83.00  
  7 purchase totals = $929.63       $1,004.0538   $1,004.04   $1,004.00   $1,004.10