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 $166.93   9.809%   $183.3042   $183.30   $183.30   $183.30  
  Purchase #2 $161.33   5.506%   $170.2128   $170.21   $170.20   $170.20  
  Purchase #3 $39.61   5.356%   $41.7315   $41.73   $41.75   $41.70  
  Purchase #4 $92.38   11.548%   $103.048   $103.05   $103.05   $103.00  
  Purchase #5 $74.72   8.276%   $80.9038   $80.90   $80.90   $80.90  
  Purchase #6 $243.83   10.418%   $269.2322   $269.23   $269.25   $269.20  
  Purchase #7 $204.37   10.449%   $225.7246   $225.72   $225.70   $225.70  
  7 purchase totals = $983.17       $1,074.1571   $1,074.14   $1,074.15   $1,074.00