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 $182.62   8.655%   $198.4258   $198.43   $198.45   $198.40  
  Purchase #2 $56.96   6.509%   $60.6675   $60.67   $60.65   $60.70  
  Purchase #3 $118.82   8.537%   $128.9637   $128.96   $128.95   $129.00  
  Purchase #4 $113.57   7.380%   $121.9515   $121.95   $121.95   $122.00  
  Purchase #5 $61.41   10.433%   $67.8169   $67.82   $67.80   $67.80  
  Purchase #6 $181.86   12.577%   $204.7325   $204.73   $204.75   $204.70  
  Purchase #7 $204.85   11.733%   $228.8851   $228.89   $228.90   $228.90  
  7 purchase totals = $920.09       $1,011.4430   $1,011.45   $1,011.45   $1,011.50