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 $67.41   12.614%   $75.9131   $75.91   $75.90   $75.90  
  Purchase #2 $160.85   11.548%   $179.425   $179.43   $179.45   $179.40  
  Purchase #3 $229.42   3.537%   $237.5346   $237.53   $237.55   $237.50  
  Purchase #4 $166.39   3.714%   $172.5697   $172.57   $172.55   $172.60  
  Purchase #5 $32.65   11.531%   $36.4149   $36.41   $36.40   $36.40  
  Purchase #6 $132.56   12.480%   $149.1035   $149.10   $149.10   $149.10  
  Purchase #7 $185.76   13.723%   $211.2518   $211.25   $211.25   $211.30  
  7 purchase totals = $975.04       $1,062.2126   $1,062.20   $1,062.20   $1,062.20