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 $68.49   3.223%   $70.6974   $70.70   $70.70   $70.70  
  Purchase #2 $60.65   6.732%   $64.733   $64.73   $64.75   $64.70  
  Purchase #3 $99.94   8.729%   $108.6638   $108.66   $108.65   $108.70  
  Purchase #4 $236.31   11.761%   $264.1024   $264.10   $264.10   $264.10  
  Purchase #5 $63.90   3.500%   $66.1365   $66.14   $66.15   $66.10  
  Purchase #6 $187.58   9.845%   $206.0473   $206.05   $206.05   $206.00  
  Purchase #7 $219.83   11.236%   $244.5301   $244.53   $244.55   $244.50  
  7 purchase totals = $936.70       $1,024.9105   $1,024.91   $1,024.95   $1,024.80