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 $90.82   11.837%   $101.5704   $101.57   $101.55   $101.60  
  Purchase #2 $118.39   4.745%   $124.0076   $124.01   $124.00   $124.00  
  Purchase #3 $22.58   12.314%   $25.3605   $25.36   $25.35   $25.40  
  Purchase #4 $233.30   6.249%   $247.8789   $247.88   $247.90   $247.90  
  Purchase #5 $22.59   4.196%   $23.5379   $23.54   $23.55   $23.50  
  Purchase #6 $200.70   12.111%   $225.0068   $225.01   $225.00   $225.00  
  Purchase #7 $107.27   5.419%   $113.083   $113.08   $113.10   $113.10  
  7 purchase totals = $795.65       $860.4451   $860.45   $860.45   $860.50