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 $173.79   3.753%   $180.3123   $180.31   $180.30   $180.30  
  Purchase #2 $212.33   8.866%   $231.1552   $231.16   $231.15   $231.20  
  Purchase #3 $216.40   3.679%   $224.3614   $224.36   $224.35   $224.40  
  Purchase #4 $13.37   6.434%   $14.2302   $14.23   $14.25   $14.20  
  Purchase #5 $7.50   12.641%   $8.4481   $8.45   $8.45   $8.40  
  Purchase #6 $19.29   4.791%   $20.2142   $20.21   $20.20   $20.20  
  Purchase #7 $106.56   5.596%   $112.5231   $112.52   $112.50   $112.50  
  7 purchase totals = $749.24       $791.2445   $791.24   $791.20   $791.20