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 $185.39   10.351%   $204.5797   $204.58   $204.60   $204.60  
  Purchase #2 $239.80   3.293%   $247.6966   $247.70   $247.70   $247.70  
  Purchase #3 $76.73   13.678%   $87.2251   $87.23   $87.25   $87.20  
  Purchase #4 $227.52   4.228%   $237.1395   $237.14   $237.15   $237.10  
  Purchase #5 $203.31   4.427%   $212.3105   $212.31   $212.30   $212.30  
  Purchase #6 $213.52   12.659%   $240.5495   $240.55   $240.55   $240.50  
  Purchase #7 $30.45   4.548%   $31.8349   $31.83   $31.85   $31.80  
  7 purchase totals = $1,176.72       $1,261.3358   $1,261.34   $1,261.40   $1,261.20