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 $217.36   6.231%   $230.9037   $230.90   $230.90   $230.90  
  Purchase #2 $60.73   4.281%   $63.3299   $63.33   $63.35   $63.30  
  Purchase #3 $192.78   4.499%   $201.4532   $201.45   $201.45   $201.50  
  Purchase #4 $23.99   12.191%   $26.9146   $26.91   $26.90   $26.90  
  Purchase #5 $135.52   6.778%   $144.7055   $144.71   $144.70   $144.70  
  Purchase #6 $244.65   3.117%   $252.2757   $252.28   $252.30   $252.30  
  Purchase #7 $20.50   7.462%   $22.0297   $22.03   $22.05   $22.00  
  7 purchase totals = $895.53       $941.6123   $941.61   $941.65   $941.60