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 $141.89   13.723%   $161.3616   $161.36   $161.35   $161.40  
  Purchase #2 $58.83   11.129%   $65.3772   $65.38   $65.40   $65.40  
  Purchase #3 $238.59   11.529%   $266.097   $266.10   $266.10   $266.10  
  Purchase #4 $26.87   6.156%   $28.5241   $28.52   $28.50   $28.50  
  Purchase #5 $173.80   11.352%   $193.5298   $193.53   $193.55   $193.50  
  Purchase #6 $212.83   11.667%   $237.6609   $237.66   $237.65   $237.70  
  Purchase #7 $224.84   6.300%   $239.0049   $239.00   $239.00   $239.00  
  7 purchase totals = $1,077.65       $1,191.5555   $1,191.55   $1,191.55   $1,191.60