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 $197.52   8.829%   $214.959   $214.96   $214.95   $215.00  
  Purchase #2 $67.83   8.740%   $73.7583   $73.76   $73.75   $73.80  
  Purchase #3 $245.74   8.533%   $266.709   $266.71   $266.70   $266.70  
  Purchase #4 $214.64   8.560%   $233.0132   $233.01   $233.00   $233.00  
  Purchase #5 $68.41   13.162%   $77.4141   $77.41   $77.40   $77.40  
  Purchase #6 $6.50   12.772%   $7.3302   $7.33   $7.35   $7.30  
  Purchase #7 $94.67   6.484%   $100.8084   $100.81   $100.80   $100.80  
  7 purchase totals = $895.31       $973.9922   $973.99   $973.95   $974.00