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 $117.53   11.514%   $131.0624   $131.06   $131.05   $131.10  
  Purchase #2 $196.63   9.867%   $216.0315   $216.03   $216.05   $216.00  
  Purchase #3 $225.48   4.816%   $236.3391   $236.34   $236.35   $236.30  
  Purchase #4 $120.30   12.179%   $134.9513   $134.95   $134.95   $135.00  
  Purchase #5 $34.68   11.330%   $38.6092   $38.61   $38.60   $38.60  
  Purchase #6 $218.37   7.804%   $235.4116   $235.41   $235.40   $235.40  
  Purchase #7 $83.88   5.397%   $88.407   $88.41   $88.40   $88.40  
  7 purchase totals = $996.87       $1,080.8121   $1,080.81   $1,080.80   $1,080.80