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 $187.52   8.411%   $203.2923   $203.29   $203.30   $203.30  
  Purchase #2 $223.28   7.619%   $240.2917   $240.29   $240.30   $240.30  
  Purchase #3 $129.76   10.492%   $143.3744   $143.37   $143.35   $143.40  
  Purchase #4 $222.60   5.195%   $234.1641   $234.16   $234.15   $234.20  
  Purchase #5 $123.99   3.214%   $127.975   $127.98   $128.00   $128.00  
  Purchase #6 $187.42   4.446%   $195.7527   $195.75   $195.75   $195.80  
  Purchase #7 $113.75   5.823%   $120.3737   $120.37   $120.35   $120.40  
  7 purchase totals = $1,188.32       $1,265.2239   $1,265.21   $1,265.20   $1,265.40