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 $15.41   7.467%   $16.5607   $16.56   $16.55   $16.60  
  Purchase #2 $193.39   4.549%   $202.1873   $202.19   $202.20   $202.20  
  Purchase #3 $216.28   6.252%   $229.8018   $229.80   $229.80   $229.80  
  Purchase #4 $11.57   4.635%   $12.1063   $12.11   $12.10   $12.10  
  Purchase #5 $24.82   7.787%   $26.7527   $26.75   $26.75   $26.80  
  Purchase #6 $32.58   10.751%   $36.0827   $36.08   $36.10   $36.10  
  Purchase #7 $195.56   6.225%   $207.7336   $207.73   $207.75   $207.70  
  7 purchase totals = $689.61       $731.2251   $731.22   $731.25   $731.30