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 $32.29   5.644%   $34.1124   $34.11   $34.10   $34.10  
  Purchase #2 $134.85   6.322%   $143.3752   $143.38   $143.40   $143.40  
  Purchase #3 $187.52   4.367%   $195.709   $195.71   $195.70   $195.70  
  Purchase #4 $55.34   8.251%   $59.9061   $59.91   $59.90   $59.90  
  Purchase #5 $157.74   5.433%   $166.31   $166.31   $166.30   $166.30  
  Purchase #6 $22.60   8.129%   $24.4372   $24.44   $24.45   $24.40  
  Purchase #7 $123.61   10.385%   $136.4469   $136.45   $136.45   $136.40  
  7 purchase totals = $713.95       $760.2968   $760.31   $760.30   $760.20