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 $61.85   11.700%   $69.0865   $69.09   $69.10   $69.10  
  Purchase #2 $53.73   12.791%   $60.6026   $60.60   $60.60   $60.60  
  Purchase #3 $205.26   11.360%   $228.5775   $228.58   $228.60   $228.60  
  Purchase #4 $168.53   4.651%   $176.3683   $176.37   $176.35   $176.40  
  Purchase #5 $23.92   3.549%   $24.7689   $24.77   $24.75   $24.80  
  Purchase #6 $189.43   11.214%   $210.6727   $210.67   $210.65   $210.70  
  Purchase #7 $228.58   7.423%   $245.5475   $245.55   $245.55   $245.50  
  7 purchase totals = $931.30       $1,015.6240   $1,015.63   $1,015.60   $1,015.70