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 $63.43   12.407%   $71.2998   $71.30   $71.30   $71.30  
  Purchase #2 $177.70   9.292%   $194.2119   $194.21   $194.20   $194.20  
  Purchase #3 $101.51   12.352%   $114.0485   $114.05   $114.05   $114.00  
  Purchase #4 $177.49   10.154%   $195.5123   $195.51   $195.50   $195.50  
  Purchase #5 $77.88   5.684%   $82.3067   $82.31   $82.30   $82.30  
  Purchase #6 $246.40   11.517%   $274.7779   $274.78   $274.80   $274.80  
  Purchase #7 $134.96   12.683%   $152.077   $152.08   $152.10   $152.10  
  7 purchase totals = $979.37       $1,084.2341   $1,084.24   $1,084.25   $1,084.20