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 $67.58   5.459%   $71.2692   $71.27   $71.25   $71.30  
  Purchase #2 $104.96   11.869%   $117.4177   $117.42   $117.40   $117.40  
  Purchase #3 $56.75   7.182%   $60.8258   $60.83   $60.85   $60.80  
  Purchase #4 $199.35   5.563%   $210.4398   $210.44   $210.45   $210.40  
  Purchase #5 $244.57   5.732%   $258.5888   $258.59   $258.60   $258.60  
  Purchase #6 $231.37   9.604%   $253.5908   $253.59   $253.60   $253.60  
  Purchase #7 $153.77   8.455%   $166.7713   $166.77   $166.75   $166.80  
  7 purchase totals = $1,058.35       $1,138.9034   $1,138.91   $1,138.90   $1,138.90