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 $202.84   6.766%   $216.5642   $216.56   $216.55   $216.60  
  Purchase #2 $51.68   6.485%   $55.0314   $55.03   $55.05   $55.00  
  Purchase #3 $220.72   3.713%   $228.9153   $228.92   $228.90   $228.90  
  Purchase #4 $217.36   3.832%   $225.6892   $225.69   $225.70   $225.70  
  Purchase #5 $86.66   13.432%   $98.3002   $98.30   $98.30   $98.30  
  Purchase #6 $16.74   5.582%   $17.6744   $17.67   $17.65   $17.70  
  Purchase #7 $203.83   9.619%   $223.4364   $223.44   $223.45   $223.40  
  7 purchase totals = $999.83       $1,065.6111   $1,065.61   $1,065.60   $1,065.60