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 $144.58   5.137%   $152.0071   $152.01   $152.00   $152.00  
  Purchase #2 $211.38   9.741%   $231.9705   $231.97   $231.95   $232.00  
  Purchase #3 $18.98   4.257%   $19.788   $19.79   $19.80   $19.80  
  Purchase #4 $232.75   6.717%   $248.3838   $248.38   $248.40   $248.40  
  Purchase #5 $167.96   7.135%   $179.9439   $179.94   $179.95   $179.90  
  Purchase #6 $250.80   3.752%   $260.21   $260.21   $260.20   $260.20  
  Purchase #7 $183.98   3.812%   $190.9933   $190.99   $191.00   $191.00  
  7 purchase totals = $1,210.43       $1,283.2966   $1,283.29   $1,283.30   $1,283.30