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 $241.81   5.184%   $254.3454   $254.35   $254.35   $254.30  
  Purchase #2 $78.79   12.274%   $88.4607   $88.46   $88.45   $88.50  
  Purchase #3 $120.27   13.561%   $136.5798   $136.58   $136.60   $136.60  
  Purchase #4 $50.70   8.268%   $54.8919   $54.89   $54.90   $54.90  
  Purchase #5 $199.91   3.368%   $206.643   $206.64   $206.65   $206.60  
  Purchase #6 $235.55   6.146%   $250.0269   $250.03   $250.05   $250.00  
  Purchase #7 $230.65   5.478%   $243.285   $243.29   $243.30   $243.30  
  7 purchase totals = $1,157.68       $1,234.2327   $1,234.24   $1,234.30   $1,234.20