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 $112.92   5.651%   $119.3011   $119.30   $119.30   $119.30  
  Purchase #2 $71.88   3.849%   $74.6467   $74.65   $74.65   $74.60  
  Purchase #3 $120.61   8.869%   $131.3069   $131.31   $131.30   $131.30  
  Purchase #4 $194.33   5.275%   $204.5809   $204.58   $204.60   $204.60  
  Purchase #5 $84.93   5.868%   $89.9137   $89.91   $89.90   $89.90  
  Purchase #6 $214.40   5.284%   $225.7289   $225.73   $225.75   $225.70  
  Purchase #7 $70.48   8.502%   $76.4722   $76.47   $76.45   $76.50  
  7 purchase totals = $869.55       $921.9504   $921.95   $921.95   $921.90