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 $55.55   9.497%   $60.8256   $60.83   $60.85   $60.80  
  Purchase #2 $125.88   6.705%   $134.3203   $134.32   $134.30   $134.30  
  Purchase #3 $199.38   7.696%   $214.7243   $214.72   $214.70   $214.70  
  Purchase #4 $45.77   11.329%   $50.9553   $50.96   $50.95   $51.00  
  Purchase #5 $235.67   7.651%   $253.7011   $253.70   $253.70   $253.70  
  Purchase #6 $191.45   10.376%   $211.3149   $211.31   $211.30   $211.30  
  Purchase #7 $93.51   4.637%   $97.8461   $97.85   $97.85   $97.80  
  7 purchase totals = $947.21       $1,023.6876   $1,023.69   $1,023.65   $1,023.60