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 $122.29   11.698%   $136.5955   $136.60   $136.60   $136.60  
  Purchase #2 $46.97   10.846%   $52.0644   $52.06   $52.05   $52.10  
  Purchase #3 $57.65   13.803%   $65.6074   $65.61   $65.60   $65.60  
  Purchase #4 $206.95   12.355%   $232.5187   $232.52   $232.50   $232.50  
  Purchase #5 $225.91   6.405%   $240.3795   $240.38   $240.40   $240.40  
  Purchase #6 $216.48   10.563%   $239.3468   $239.35   $239.35   $239.30  
  Purchase #7 $212.48   10.199%   $234.1508   $234.15   $234.15   $234.20  
  7 purchase totals = $1,088.73       $1,200.6631   $1,200.67   $1,200.65   $1,200.70