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 $58.44   8.779%   $63.5704   $63.57   $63.55   $63.60  
  Purchase #2 $66.49   9.201%   $72.6077   $72.61   $72.60   $72.60  
  Purchase #3 $105.85   10.263%   $116.7134   $116.71   $116.70   $116.70  
  Purchase #4 $208.46   12.864%   $235.2763   $235.28   $235.30   $235.30  
  Purchase #5 $66.59   8.245%   $72.0803   $72.08   $72.10   $72.10  
  Purchase #6 $45.53   9.270%   $49.7506   $49.75   $49.75   $49.80  
  Purchase #7 $130.39   11.321%   $145.1515   $145.15   $145.15   $145.20  
  7 purchase totals = $681.75       $755.1502   $755.15   $755.15   $755.30