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 $177.98   10.151%   $196.0467   $196.05   $196.05   $196.00  
  Purchase #2 $55.35   11.703%   $61.8276   $61.83   $61.85   $61.80  
  Purchase #3 $202.52   9.464%   $221.6865   $221.69   $221.70   $221.70  
  Purchase #4 $29.27   13.618%   $33.256   $33.26   $33.25   $33.30  
  Purchase #5 $174.92   6.623%   $186.505   $186.51   $186.50   $186.50  
  Purchase #6 $182.88   5.368%   $192.697   $192.70   $192.70   $192.70  
  Purchase #7 $154.97   12.731%   $174.6992   $174.70   $174.70   $174.70  
  7 purchase totals = $977.89       $1,066.7180   $1,066.74   $1,066.75   $1,066.70