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 $65.62   4.663%   $68.6799   $68.68   $68.70   $68.70  
  Purchase #2 $202.33   7.760%   $218.0308   $218.03   $218.05   $218.00  
  Purchase #3 $156.32   12.628%   $176.0601   $176.06   $176.05   $176.10  
  Purchase #4 $5.71   3.751%   $5.9242   $5.92   $5.90   $5.90  
  Purchase #5 $204.70   6.511%   $218.028   $218.03   $218.05   $218.00  
  Purchase #6 $92.54   7.768%   $99.7285   $99.73   $99.75   $99.70  
  Purchase #7 $150.37   13.728%   $171.0128   $171.01   $171.00   $171.00  
  7 purchase totals = $877.59       $957.4643   $957.46   $957.50   $957.40