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 $184.28   8.148%   $199.2951   $199.30   $199.30   $199.30  
  Purchase #2 $229.59   7.554%   $246.9332   $246.93   $246.95   $246.90  
  Purchase #3 $222.87   5.575%   $235.295   $235.30   $235.30   $235.30  
  Purchase #4 $60.52   6.843%   $64.6614   $64.66   $64.65   $64.70  
  Purchase #5 $121.71   4.851%   $127.6142   $127.61   $127.60   $127.60  
  Purchase #6 $120.69   13.546%   $137.0387   $137.04   $137.05   $137.00  
  Purchase #7 $166.59   13.247%   $188.6582   $188.66   $188.65   $188.70  
  7 purchase totals = $1,106.25       $1,199.4958   $1,199.50   $1,199.50   $1,199.50