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 $164.48   13.139%   $186.091   $186.09   $186.10   $186.10  
  Purchase #2 $128.89   7.155%   $138.1121   $138.11   $138.10   $138.10  
  Purchase #3 $76.91   11.103%   $85.4493   $85.45   $85.45   $85.40  
  Purchase #4 $246.96   10.843%   $273.7379   $273.74   $273.75   $273.70  
  Purchase #5 $233.89   8.445%   $253.642   $253.64   $253.65   $253.60  
  Purchase #6 $190.52   11.228%   $211.9116   $211.91   $211.90   $211.90  
  Purchase #7 $22.52   4.775%   $23.5953   $23.60   $23.60   $23.60  
  7 purchase totals = $1,064.17       $1,172.5392   $1,172.54   $1,172.55   $1,172.40