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 $112.53   6.272%   $119.5879   $119.59   $119.60   $119.60  
  Purchase #2 $74.38   7.612%   $80.0418   $80.04   $80.05   $80.00  
  Purchase #3 $176.34   4.321%   $183.9597   $183.96   $183.95   $184.00  
  Purchase #4 $71.30   4.187%   $74.2853   $74.29   $74.30   $74.30  
  Purchase #5 $50.57   11.668%   $56.4705   $56.47   $56.45   $56.50  
  Purchase #6 $244.55   12.290%   $274.6052   $274.61   $274.60   $274.60  
  Purchase #7 $22.80   5.336%   $24.0166   $24.02   $24.00   $24.00  
  7 purchase totals = $752.47       $812.9670   $812.98   $812.95   $813.00