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 $39.94   12.614%   $44.978   $44.98   $45.00   $45.00  
  Purchase #2 $60.79   8.125%   $65.7292   $65.73   $65.75   $65.70  
  Purchase #3 $158.66   4.863%   $166.3756   $166.38   $166.40   $166.40  
  Purchase #4 $209.27   6.805%   $223.5108   $223.51   $223.50   $223.50  
  Purchase #5 $127.73   6.272%   $135.7412   $135.74   $135.75   $135.70  
  Purchase #6 $198.87   11.656%   $222.0503   $222.05   $222.05   $222.10  
  Purchase #7 $35.43   3.720%   $36.748   $36.75   $36.75   $36.70  
  7 purchase totals = $830.69       $895.1331   $895.14   $895.20   $895.10