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 $155.62   11.108%   $172.9063   $172.91   $172.90   $172.90  
  Purchase #2 $232.81   6.391%   $247.6889   $247.69   $247.70   $247.70  
  Purchase #3 $140.34   10.666%   $155.3087   $155.31   $155.30   $155.30  
  Purchase #4 $153.59   13.317%   $174.0436   $174.04   $174.05   $174.00  
  Purchase #5 $43.37   3.107%   $44.7175   $44.72   $44.70   $44.70  
  Purchase #6 $200.41   4.144%   $208.715   $208.72   $208.70   $208.70  
  Purchase #7 $20.28   5.754%   $21.4469   $21.45   $21.45   $21.40  
  7 purchase totals = $946.42       $1,024.8269   $1,024.84   $1,024.80   $1,024.70