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 $209.98   10.746%   $232.5445   $232.54   $232.55   $232.50  
  Purchase #2 $124.29   9.495%   $136.0913   $136.09   $136.10   $136.10  
  Purchase #3 $109.55   8.219%   $118.5539   $118.55   $118.55   $118.60  
  Purchase #4 $69.39   11.259%   $77.2026   $77.20   $77.20   $77.20  
  Purchase #5 $36.97   13.182%   $41.8434   $41.84   $41.85   $41.80  
  Purchase #6 $221.37   13.780%   $251.8748   $251.87   $251.85   $251.90  
  Purchase #7 $166.49   3.550%   $172.4004   $172.40   $172.40   $172.40  
  7 purchase totals = $938.04       $1,030.5109   $1,030.49   $1,030.50   $1,030.50