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 $119.35   4.731%   $124.9964   $125.00   $125.00   $125.00  
  Purchase #2 $75.42   9.611%   $82.6686   $82.67   $82.65   $82.70  
  Purchase #3 $104.98   11.626%   $117.185   $117.19   $117.20   $117.20  
  Purchase #4 $22.88   13.264%   $25.9148   $25.91   $25.90   $25.90  
  Purchase #5 $198.77   12.235%   $223.0895   $223.09   $223.10   $223.10  
  Purchase #6 $238.83   12.221%   $268.0174   $268.02   $268.00   $268.00  
  Purchase #7 $135.56   8.874%   $147.5896   $147.59   $147.60   $147.60  
  7 purchase totals = $895.79       $989.4613   $989.47   $989.45   $989.50