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 $88.71   5.138%   $93.2679   $93.27   $93.25   $93.30  
  Purchase #2 $182.74   6.423%   $194.4774   $194.48   $194.50   $194.50  
  Purchase #3 $70.47   13.846%   $80.2273   $80.23   $80.25   $80.20  
  Purchase #4 $133.31   5.794%   $141.034   $141.03   $141.05   $141.00  
  Purchase #5 $43.37   6.442%   $46.1639   $46.16   $46.15   $46.20  
  Purchase #6 $178.37   12.324%   $200.3523   $200.35   $200.35   $200.40  
  Purchase #7 $181.79   5.834%   $192.3956   $192.40   $192.40   $192.40  
  7 purchase totals = $878.76       $947.9184   $947.92   $947.95   $948.00