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 $147.47   6.377%   $156.8742   $156.87   $156.85   $156.90  
  Purchase #2 $216.50   11.608%   $241.6313   $241.63   $241.65   $241.60  
  Purchase #3 $133.30   6.234%   $141.6099   $141.61   $141.60   $141.60  
  Purchase #4 $134.99   9.458%   $147.7574   $147.76   $147.75   $147.80  
  Purchase #5 $203.26   7.713%   $218.9374   $218.94   $218.95   $218.90  
  Purchase #6 $157.81   5.819%   $166.993   $166.99   $167.00   $167.00  
  Purchase #7 $8.65   4.289%   $9.021   $9.02   $9.00   $9.00  
  7 purchase totals = $1,001.98       $1,082.8242   $1,082.82   $1,082.80   $1,082.80