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 $104.44   5.779%   $110.4756   $110.48   $110.50   $110.50  
  Purchase #2 $160.94   12.656%   $181.3086   $181.31   $181.30   $181.30  
  Purchase #3 $66.99   10.483%   $74.0126   $74.01   $74.00   $74.00  
  Purchase #4 $250.64   13.168%   $283.6443   $283.64   $283.65   $283.60  
  Purchase #5 $173.25   12.812%   $195.4468   $195.45   $195.45   $195.40  
  Purchase #6 $51.39   10.776%   $56.9278   $56.93   $56.95   $56.90  
  Purchase #7 $107.35   11.232%   $119.4076   $119.41   $119.40   $119.40  
  7 purchase totals = $915.00       $1,021.2233   $1,021.23   $1,021.25   $1,021.10