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 $181.95   11.608%   $203.0708   $203.07   $203.05   $203.10  
  Purchase #2 $153.29   12.726%   $172.7977   $172.80   $172.80   $172.80  
  Purchase #3 $207.65   13.395%   $235.4647   $235.46   $235.45   $235.50  
  Purchase #4 $86.36   11.649%   $96.4201   $96.42   $96.40   $96.40  
  Purchase #5 $181.49   11.646%   $202.6263   $202.63   $202.65   $202.60  
  Purchase #6 $102.80   11.671%   $114.7978   $114.80   $114.80   $114.80  
  Purchase #7 $62.28   11.310%   $69.3239   $69.32   $69.30   $69.30  
  7 purchase totals = $975.82       $1,094.5013   $1,094.50   $1,094.45   $1,094.50