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 $63.82   9.435%   $69.8414   $69.84   $69.85   $69.80  
  Purchase #2 $88.26   5.541%   $93.1505   $93.15   $93.15   $93.20  
  Purchase #3 $236.59   6.756%   $252.574   $252.57   $252.55   $252.60  
  Purchase #4 $160.76   5.443%   $169.5102   $169.51   $169.50   $169.50  
  Purchase #5 $167.52   7.857%   $180.682   $180.68   $180.70   $180.70  
  Purchase #6 $215.40   12.371%   $242.0471   $242.05   $242.05   $242.00  
  Purchase #7 $182.47   3.462%   $188.7871   $188.79   $188.80   $188.80  
  7 purchase totals = $1,114.82       $1,196.5923   $1,196.59   $1,196.60   $1,196.60