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 $65.35   13.671%   $74.284   $74.28   $74.30   $74.30  
  Purchase #2 $166.65   3.726%   $172.8594   $172.86   $172.85   $172.90  
  Purchase #3 $135.98   12.212%   $152.5859   $152.59   $152.60   $152.60  
  Purchase #4 $187.99   3.118%   $193.8515   $193.85   $193.85   $193.90  
  Purchase #5 $183.50   6.700%   $195.7945   $195.79   $195.80   $195.80  
  Purchase #6 $103.93   6.691%   $110.884   $110.88   $110.90   $110.90  
  Purchase #7 $147.81   10.694%   $163.6168   $163.62   $163.60   $163.60  
  7 purchase totals = $991.21       $1,063.8761   $1,063.87   $1,063.90   $1,064.00