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 $134.93   13.176%   $152.7084   $152.71   $152.70   $152.70  
  Purchase #2 $161.47   5.207%   $169.8777   $169.88   $169.90   $169.90  
  Purchase #3 $15.76   13.137%   $17.8304   $17.83   $17.85   $17.80  
  Purchase #4 $192.36   5.185%   $202.3339   $202.33   $202.35   $202.30  
  Purchase #5 $162.89   5.571%   $171.9646   $171.96   $171.95   $172.00  
  Purchase #6 $199.56   12.858%   $225.2194   $225.22   $225.20   $225.20  
  Purchase #7 $105.96   13.608%   $120.379   $120.38   $120.40   $120.40  
  7 purchase totals = $972.93       $1,060.3134   $1,060.31   $1,060.35   $1,060.30