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 $57.61   3.432%   $59.5872   $59.59   $59.60   $59.60  
  Purchase #2 $145.81   13.223%   $165.0905   $165.09   $165.10   $165.10  
  Purchase #3 $62.37   3.694%   $64.6739   $64.67   $64.65   $64.70  
  Purchase #4 $240.32   12.216%   $269.6775   $269.68   $269.70   $269.70  
  Purchase #5 $68.92   6.165%   $73.1689   $73.17   $73.15   $73.20  
  Purchase #6 $235.73   3.744%   $244.5557   $244.56   $244.55   $244.60  
  Purchase #7 $109.45   9.315%   $119.6453   $119.65   $119.65   $119.60  
  7 purchase totals = $920.21       $996.3990   $996.41   $996.40   $996.50