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 $181.58   11.394%   $202.2692   $202.27   $202.25   $202.30  
  Purchase #2 $11.47   6.291%   $12.1916   $12.19   $12.20   $12.20  
  Purchase #3 $60.84   11.700%   $67.9583   $67.96   $67.95   $68.00  
  Purchase #4 $186.25   5.670%   $196.8104   $196.81   $196.80   $196.80  
  Purchase #5 $113.69   11.682%   $126.9713   $126.97   $126.95   $127.00  
  Purchase #6 $250.36   13.430%   $283.9833   $283.98   $284.00   $284.00  
  Purchase #7 $139.69   9.253%   $152.6155   $152.62   $152.60   $152.60  
  7 purchase totals = $943.88       $1,042.7996   $1,042.80   $1,042.75   $1,042.90