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 $223.84   7.735%   $241.154   $241.15   $241.15   $241.20  
  Purchase #2 $166.97   8.429%   $181.0439   $181.04   $181.05   $181.00  
  Purchase #3 $34.31   6.731%   $36.6194   $36.62   $36.60   $36.60  
  Purchase #4 $111.42   11.269%   $123.9759   $123.98   $124.00   $124.00  
  Purchase #5 $207.33   7.306%   $222.4775   $222.48   $222.50   $222.50  
  Purchase #6 $26.80   4.498%   $28.0055   $28.01   $28.00   $28.00  
  Purchase #7 $165.87   7.861%   $178.909   $178.91   $178.90   $178.90  
  7 purchase totals = $936.54       $1,012.1852   $1,012.19   $1,012.20   $1,012.20