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 $61.73   5.412%   $65.0708   $65.07   $65.05   $65.10  
  Purchase #2 $202.70   10.104%   $223.1808   $223.18   $223.20   $223.20  
  Purchase #3 $186.94   8.346%   $202.542   $202.54   $202.55   $202.50  
  Purchase #4 $136.90   11.538%   $152.6955   $152.70   $152.70   $152.70  
  Purchase #5 $73.96   10.277%   $81.5609   $81.56   $81.55   $81.60  
  Purchase #6 $146.83   5.696%   $155.1934   $155.19   $155.20   $155.20  
  Purchase #7 $219.90   10.829%   $243.713   $243.71   $243.70   $243.70  
  7 purchase totals = $1,028.96       $1,123.9564   $1,123.95   $1,123.95   $1,124.00