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 $49.31   7.606%   $53.0605   $53.06   $53.05   $53.10  
  Purchase #2 $160.37   4.236%   $167.1633   $167.16   $167.15   $167.20  
  Purchase #3 $223.56   10.300%   $246.5867   $246.59   $246.60   $246.60  
  Purchase #4 $68.70   10.641%   $76.0104   $76.01   $76.00   $76.00  
  Purchase #5 $183.36   11.111%   $203.7331   $203.73   $203.75   $203.70  
  Purchase #6 $145.81   11.826%   $163.0535   $163.05   $163.05   $163.10  
  Purchase #7 $61.79   6.849%   $66.022   $66.02   $66.00   $66.00  
  7 purchase totals = $892.90       $975.6295   $975.62   $975.60   $975.70