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 $183.93   12.705%   $207.2983   $207.30   $207.30   $207.30  
  Purchase #2 $83.86   13.135%   $94.875   $94.88   $94.90   $94.90  
  Purchase #3 $70.36   4.496%   $73.5234   $73.52   $73.50   $73.50  
  Purchase #4 $65.82   12.132%   $73.8053   $73.81   $73.80   $73.80  
  Purchase #5 $176.68   11.265%   $196.583   $196.58   $196.60   $196.60  
  Purchase #6 $15.30   7.497%   $16.447   $16.45   $16.45   $16.40  
  Purchase #7 $181.50   12.565%   $204.3055   $204.31   $204.30   $204.30  
  7 purchase totals = $777.45       $866.8375   $866.85   $866.85   $866.80