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 $153.81   13.735%   $174.9358   $174.94   $174.95   $174.90  
  Purchase #2 $169.64   6.566%   $180.7786   $180.78   $180.80   $180.80  
  Purchase #3 $49.33   6.320%   $52.4477   $52.45   $52.45   $52.40  
  Purchase #4 $13.91   9.458%   $15.2256   $15.23   $15.25   $15.20  
  Purchase #5 $219.69   5.459%   $231.6829   $231.68   $231.70   $231.70  
  Purchase #6 $215.57   10.642%   $238.511   $238.51   $238.50   $238.50  
  Purchase #7 $145.49   7.460%   $156.3436   $156.34   $156.35   $156.30  
  7 purchase totals = $967.44       $1,049.9252   $1,049.93   $1,050.00   $1,049.80