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 $107.52   8.314%   $116.4592   $116.46   $116.45   $116.50  
  Purchase #2 $192.62   5.665%   $203.5319   $203.53   $203.55   $203.50  
  Purchase #3 $234.62   3.638%   $243.1555   $243.16   $243.15   $243.20  
  Purchase #4 $61.77   8.508%   $67.0254   $67.03   $67.05   $67.00  
  Purchase #5 $191.95   11.196%   $213.4407   $213.44   $213.45   $213.40  
  Purchase #6 $213.73   13.157%   $241.8505   $241.85   $241.85   $241.90  
  Purchase #7 $77.31   13.630%   $87.8474   $87.85   $87.85   $87.80  
  7 purchase totals = $1,079.52       $1,173.3106   $1,173.32   $1,173.35   $1,173.30