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 $148.86   11.713%   $166.296   $166.30   $166.30   $166.30  
  Purchase #2 $95.25   8.127%   $102.991   $102.99   $103.00   $103.00  
  Purchase #3 $84.66   10.586%   $93.6221   $93.62   $93.60   $93.60  
  Purchase #4 $172.79   13.495%   $196.108   $196.11   $196.10   $196.10  
  Purchase #5 $65.72   12.117%   $73.6833   $73.68   $73.70   $73.70  
  Purchase #6 $122.81   3.432%   $127.0248   $127.02   $127.00   $127.00  
  Purchase #7 $157.57   12.415%   $177.1323   $177.13   $177.15   $177.10  
  7 purchase totals = $847.66       $936.8575   $936.85   $936.85   $936.80