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 $60.65   9.746%   $66.5609   $66.56   $66.55   $66.60  
  Purchase #2 $35.92   3.671%   $37.2386   $37.24   $37.25   $37.20  
  Purchase #3 $186.98   9.526%   $204.7917   $204.79   $204.80   $204.80  
  Purchase #4 $30.53   9.452%   $33.4157   $33.42   $33.40   $33.40  
  Purchase #5 $193.77   5.787%   $204.9835   $204.98   $205.00   $205.00  
  Purchase #6 $75.92   6.437%   $80.807   $80.81   $80.80   $80.80  
  Purchase #7 $194.57   5.283%   $204.8491   $204.85   $204.85   $204.80  
  7 purchase totals = $778.34       $832.6465   $832.65   $832.65   $832.60