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 $194.98   5.819%   $206.3259   $206.33   $206.35   $206.30  
  Purchase #2 $29.85   9.845%   $32.7887   $32.79   $32.80   $32.80  
  Purchase #3 $218.79   3.112%   $225.5987   $225.60   $225.60   $225.60  
  Purchase #4 $97.85   10.645%   $108.2661   $108.27   $108.25   $108.30  
  Purchase #5 $104.56   4.495%   $109.26   $109.26   $109.25   $109.30  
  Purchase #6 $118.31   10.211%   $130.3906   $130.39   $130.40   $130.40  
  Purchase #7 $163.62   9.504%   $179.1704   $179.17   $179.15   $179.20  
  7 purchase totals = $927.96       $991.8004   $991.81   $991.80   $991.90