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 $209.45   11.774%   $234.1106   $234.11   $234.10   $234.10  
  Purchase #2 $60.27   12.546%   $67.8315   $67.83   $67.85   $67.80  
  Purchase #3 $218.60   10.560%   $241.6842   $241.68   $241.70   $241.70  
  Purchase #4 $168.75   12.467%   $189.7881   $189.79   $189.80   $189.80  
  Purchase #5 $112.72   13.542%   $127.9845   $127.98   $128.00   $128.00  
  Purchase #6 $107.87   4.180%   $112.379   $112.38   $112.40   $112.40  
  Purchase #7 $118.33   13.495%   $134.2986   $134.30   $134.30   $134.30  
  7 purchase totals = $995.99       $1,108.0765   $1,108.07   $1,108.15   $1,108.10