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 $89.66   13.167%   $101.4655   $101.47   $101.45   $101.50  
  Purchase #2 $201.69   4.726%   $211.2219   $211.22   $211.20   $211.20  
  Purchase #3 $124.48   8.802%   $135.4367   $135.44   $135.45   $135.40  
  Purchase #4 $226.32   9.232%   $247.2139   $247.21   $247.20   $247.20  
  Purchase #5 $118.29   6.574%   $126.0664   $126.07   $126.05   $126.10  
  Purchase #6 $238.69   11.623%   $266.4329   $266.43   $266.45   $266.40  
  Purchase #7 $73.70   9.432%   $80.6514   $80.65   $80.65   $80.70  
  7 purchase totals = $1,072.83       $1,168.4887   $1,168.49   $1,168.45   $1,168.50