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 $49.51   11.701%   $55.3032   $55.30   $55.30   $55.30  
  Purchase #2 $165.47   8.502%   $179.5383   $179.54   $179.55   $179.50  
  Purchase #3 $210.70   10.267%   $232.3326   $232.33   $232.35   $232.30  
  Purchase #4 $148.95   8.666%   $161.858   $161.86   $161.85   $161.90  
  Purchase #5 $137.44   12.407%   $154.4922   $154.49   $154.50   $154.50  
  Purchase #6 $246.25   12.164%   $276.2039   $276.20   $276.20   $276.20  
  Purchase #7 $34.47   7.433%   $37.0322   $37.03   $37.05   $37.00  
  7 purchase totals = $992.79       $1,096.7604   $1,096.75   $1,096.80   $1,096.70