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 $90.38   6.341%   $96.111   $96.11   $96.10   $96.10  
  Purchase #2 $31.32   11.735%   $34.9954   $35.00   $35.00   $35.00  
  Purchase #3 $203.95   3.780%   $211.6593   $211.66   $211.65   $211.70  
  Purchase #4 $246.49   7.354%   $264.6169   $264.62   $264.60   $264.60  
  Purchase #5 $49.79   13.317%   $56.4205   $56.42   $56.40   $56.40  
  Purchase #6 $194.27   5.508%   $204.9704   $204.97   $204.95   $205.00  
  Purchase #7 $24.37   9.605%   $26.7107   $26.71   $26.70   $26.70  
  7 purchase totals = $840.57       $895.4842   $895.49   $895.40   $895.50