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 $113.41   5.658%   $119.8267   $119.83   $119.85   $119.80  
  Purchase #2 $233.82   10.153%   $257.5597   $257.56   $257.55   $257.60  
  Purchase #3 $65.54   4.769%   $68.6656   $68.67   $68.65   $68.70  
  Purchase #4 $83.47   12.114%   $93.5816   $93.58   $93.60   $93.60  
  Purchase #5 $181.64   5.709%   $192.0098   $192.01   $192.00   $192.00  
  Purchase #6 $115.52   12.117%   $129.5176   $129.52   $129.50   $129.50  
  Purchase #7 $77.74   5.297%   $81.8579   $81.86   $81.85   $81.90  
  7 purchase totals = $871.14       $943.0189   $943.03   $943.00   $943.10