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 $78.38   11.154%   $87.1225   $87.12   $87.10   $87.10  
  Purchase #2 $191.58   6.776%   $204.5615   $204.56   $204.55   $204.60  
  Purchase #3 $166.38   12.292%   $186.8314   $186.83   $186.85   $186.80  
  Purchase #4 $65.66   12.845%   $74.094   $74.09   $74.10   $74.10  
  Purchase #5 $60.52   4.122%   $63.0146   $63.01   $63.00   $63.00  
  Purchase #6 $161.49   13.469%   $183.2411   $183.24   $183.25   $183.20  
  Purchase #7 $214.54   10.565%   $237.2062   $237.21   $237.20   $237.20  
  7 purchase totals = $938.55       $1,036.0713   $1,036.06   $1,036.05   $1,036.00