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 $193.39   9.517%   $211.7949   $211.79   $211.80   $211.80  
  Purchase #2 $37.33   8.135%   $40.3668   $40.37   $40.35   $40.40  
  Purchase #3 $101.63   12.107%   $113.9343   $113.93   $113.95   $113.90  
  Purchase #4 $234.49   9.505%   $256.7783   $256.78   $256.80   $256.80  
  Purchase #5 $229.93   6.866%   $245.717   $245.72   $245.70   $245.70  
  Purchase #6 $60.35   10.451%   $66.6572   $66.66   $66.65   $66.70  
  Purchase #7 $118.95   4.183%   $123.9257   $123.93   $123.95   $123.90  
  7 purchase totals = $976.07       $1,059.1742   $1,059.18   $1,059.20   $1,059.20