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 $54.29   12.502%   $61.0773   $61.08   $61.10   $61.10  
  Purchase #2 $222.61   4.752%   $233.1884   $233.19   $233.20   $233.20  
  Purchase #3 $189.93   6.403%   $202.0912   $202.09   $202.10   $202.10  
  Purchase #4 $220.37   10.289%   $243.0439   $243.04   $243.05   $243.00  
  Purchase #5 $39.68   9.626%   $43.4996   $43.50   $43.50   $43.50  
  Purchase #6 $24.42   7.461%   $26.242   $26.24   $26.25   $26.20  
  Purchase #7 $86.58   6.561%   $92.2605   $92.26   $92.25   $92.30  
  7 purchase totals = $837.88       $901.4029   $901.40   $901.45   $901.40