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 $105.75   10.513%   $116.8675   $116.87   $116.85   $116.90  
  Purchase #2 $60.62   10.411%   $66.9311   $66.93   $66.95   $66.90  
  Purchase #3 $151.88   11.235%   $168.9437   $168.94   $168.95   $168.90  
  Purchase #4 $78.73   12.626%   $88.6704   $88.67   $88.65   $88.70  
  Purchase #5 $216.96   12.519%   $244.1212   $244.12   $244.10   $244.10  
  Purchase #6 $175.94   12.685%   $198.258   $198.26   $198.25   $198.30  
  Purchase #7 $171.70   7.627%   $184.7956   $184.80   $184.80   $184.80  
  7 purchase totals = $961.58       $1,068.5875   $1,068.59   $1,068.55   $1,068.60