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 $124.51   8.444%   $135.0236   $135.02   $135.00   $135.00  
  Purchase #2 $216.62   9.854%   $237.9657   $237.97   $237.95   $238.00  
  Purchase #3 $11.72   13.791%   $13.3363   $13.34   $13.35   $13.30  
  Purchase #4 $250.62   3.166%   $258.5546   $258.55   $258.55   $258.60  
  Purchase #5 $99.91   10.364%   $110.2647   $110.26   $110.25   $110.30  
  Purchase #6 $172.79   6.832%   $184.595   $184.60   $184.60   $184.60  
  Purchase #7 $126.71   7.604%   $136.345   $136.35   $136.35   $136.30  
  7 purchase totals = $1,002.88       $1,076.0849   $1,076.09   $1,076.05   $1,076.10