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 $181.86   6.664%   $193.9792   $193.98   $194.00   $194.00  
  Purchase #2 $242.64   13.537%   $275.4862   $275.49   $275.50   $275.50  
  Purchase #3 $185.32   13.586%   $210.4976   $210.50   $210.50   $210.50  
  Purchase #4 $223.56   8.690%   $242.9874   $242.99   $243.00   $243.00  
  Purchase #5 $24.53   8.720%   $26.669   $26.67   $26.65   $26.70  
  Purchase #6 $113.35   6.517%   $120.737   $120.74   $120.75   $120.70  
  Purchase #7 $203.94   11.318%   $227.0219   $227.02   $227.00   $227.00  
  7 purchase totals = $1,175.20       $1,297.3783   $1,297.39   $1,297.40   $1,297.40