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 $244.33   8.339%   $264.7047   $264.70   $264.70   $264.70  
  Purchase #2 $92.82   8.220%   $100.4498   $100.45   $100.45   $100.40  
  Purchase #3 $113.66   4.814%   $119.1316   $119.13   $119.15   $119.10  
  Purchase #4 $64.44   12.746%   $72.6535   $72.65   $72.65   $72.70  
  Purchase #5 $69.59   5.590%   $73.4801   $73.48   $73.50   $73.50  
  Purchase #6 $220.66   10.136%   $243.0261   $243.03   $243.05   $243.00  
  Purchase #7 $208.50   8.424%   $226.064   $226.06   $226.05   $226.10  
  7 purchase totals = $1,014.00       $1,099.5098   $1,099.50   $1,099.55   $1,099.50