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 $61.80   3.143%   $63.7424   $63.74   $63.75   $63.70  
  Purchase #2 $244.32   8.346%   $264.7109   $264.71   $264.70   $264.70  
  Purchase #3 $59.87   10.344%   $66.063   $66.06   $66.05   $66.10  
  Purchase #4 $220.28   10.350%   $243.079   $243.08   $243.10   $243.10  
  Purchase #5 $214.48   11.267%   $238.6455   $238.65   $238.65   $238.60  
  Purchase #6 $17.48   12.449%   $19.6561   $19.66   $19.65   $19.70  
  Purchase #7 $113.47   13.410%   $128.6863   $128.69   $128.70   $128.70  
  7 purchase totals = $931.70       $1,024.5832   $1,024.59   $1,024.60   $1,024.60