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 $62.82   11.781%   $70.2208   $70.22   $70.20   $70.20  
  Purchase #2 $25.85   7.102%   $27.6859   $27.69   $27.70   $27.70  
  Purchase #3 $216.91   9.668%   $237.8809   $237.88   $237.90   $237.90  
  Purchase #4 $165.27   8.865%   $179.9212   $179.92   $179.90   $179.90  
  Purchase #5 $134.54   8.300%   $145.7068   $145.71   $145.70   $145.70  
  Purchase #6 $143.95   4.228%   $150.0362   $150.04   $150.05   $150.00  
  Purchase #7 $129.74   7.355%   $139.2824   $139.28   $139.30   $139.30  
  7 purchase totals = $879.08       $950.7342   $950.74   $950.75   $950.70