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 $154.47   11.402%   $172.0827   $172.08   $172.10   $172.10  
  Purchase #2 $219.97   10.759%   $243.6366   $243.64   $243.65   $243.60  
  Purchase #3 $61.76   6.450%   $65.7435   $65.74   $65.75   $65.70  
  Purchase #4 $30.84   11.491%   $34.3838   $34.38   $34.40   $34.40  
  Purchase #5 $115.80   12.466%   $130.2356   $130.24   $130.25   $130.20  
  Purchase #6 $82.47   5.310%   $86.8492   $86.85   $86.85   $86.80  
  Purchase #7 $41.29   4.666%   $43.2166   $43.22   $43.20   $43.20  
  7 purchase totals = $706.60       $776.1480   $776.15   $776.20   $776.00