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 $65.89   7.493%   $70.8271   $70.83   $70.85   $70.80  
  Purchase #2 $206.43   12.363%   $231.9509   $231.95   $231.95   $232.00  
  Purchase #3 $84.39   6.816%   $90.142   $90.14   $90.15   $90.10  
  Purchase #4 $103.93   10.178%   $114.508   $114.51   $114.50   $114.50  
  Purchase #5 $215.34   7.457%   $231.3979   $231.40   $231.40   $231.40  
  Purchase #6 $233.75   11.518%   $260.6733   $260.67   $260.65   $260.70  
  Purchase #7 $188.53   8.825%   $205.1678   $205.17   $205.15   $205.20  
  7 purchase totals = $1,098.26       $1,204.6670   $1,204.67   $1,204.65   $1,204.70