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 $203.86   10.641%   $225.5527   $225.55   $225.55   $225.60  
  Purchase #2 $182.97   6.333%   $194.5575   $194.56   $194.55   $194.60  
  Purchase #3 $10.90   6.526%   $11.6113   $11.61   $11.60   $11.60  
  Purchase #4 $180.99   11.520%   $201.84   $201.84   $201.85   $201.80  
  Purchase #5 $72.85   11.126%   $80.9553   $80.96   $80.95   $81.00  
  Purchase #6 $220.36   7.151%   $236.1179   $236.12   $236.10   $236.10  
  Purchase #7 $211.83   5.837%   $224.1945   $224.19   $224.20   $224.20  
  7 purchase totals = $1,083.76       $1,174.8292   $1,174.83   $1,174.80   $1,174.90