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 $93.41   9.478%   $102.2634   $102.26   $102.25   $102.30  
  Purchase #2 $206.77   7.730%   $222.7533   $222.75   $222.75   $222.80  
  Purchase #3 $203.31   7.442%   $218.4403   $218.44   $218.45   $218.40  
  Purchase #4 $95.35   4.425%   $99.5692   $99.57   $99.55   $99.60  
  Purchase #5 $199.99   13.422%   $226.8327   $226.83   $226.85   $226.80  
  Purchase #6 $234.52   8.253%   $253.8749   $253.87   $253.85   $253.90  
  Purchase #7 $124.25   12.268%   $139.493   $139.49   $139.50   $139.50  
  7 purchase totals = $1,157.60       $1,263.2268   $1,263.21   $1,263.20   $1,263.30