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 $60.32   12.869%   $68.0826   $68.08   $68.10   $68.10  
  Purchase #2 $48.27   9.512%   $52.8614   $52.86   $52.85   $52.90  
  Purchase #3 $245.78   12.551%   $276.6278   $276.63   $276.65   $276.60  
  Purchase #4 $206.65   8.211%   $223.618   $223.62   $223.60   $223.60  
  Purchase #5 $43.33   10.204%   $47.7514   $47.75   $47.75   $47.80  
  Purchase #6 $13.44   4.459%   $14.0393   $14.04   $14.05   $14.00  
  Purchase #7 $159.77   6.578%   $170.2797   $170.28   $170.30   $170.30  
  7 purchase totals = $777.56       $853.2602   $853.26   $853.30   $853.30