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 $164.88   13.187%   $186.6227   $186.62   $186.60   $186.60  
  Purchase #2 $192.85   5.749%   $203.9369   $203.94   $203.95   $203.90  
  Purchase #3 $93.84   13.517%   $106.5244   $106.52   $106.50   $106.50  
  Purchase #4 $207.46   3.560%   $214.8456   $214.85   $214.85   $214.80  
  Purchase #5 $225.59   11.107%   $250.6463   $250.65   $250.65   $250.60  
  Purchase #6 $35.97   7.774%   $38.7663   $38.77   $38.75   $38.80  
  Purchase #7 $231.66   4.842%   $242.877   $242.88   $242.90   $242.90  
  7 purchase totals = $1,152.25       $1,244.2192   $1,244.23   $1,244.20   $1,244.10