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 $141.76   8.339%   $153.5814   $153.58   $153.60   $153.60  
  Purchase #2 $51.70   13.653%   $58.7586   $58.76   $58.75   $58.80  
  Purchase #3 $209.61   8.218%   $226.8357   $226.84   $226.85   $226.80  
  Purchase #4 $33.31   8.520%   $36.148   $36.15   $36.15   $36.10  
  Purchase #5 $232.87   4.685%   $243.78   $243.78   $243.80   $243.80  
  Purchase #6 $100.59   12.348%   $113.0109   $113.01   $113.00   $113.00  
  Purchase #7 $226.79   6.752%   $242.1029   $242.10   $242.10   $242.10  
  7 purchase totals = $996.63       $1,074.2175   $1,074.22   $1,074.25   $1,074.20