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 $147.70   3.136%   $152.3319   $152.33   $152.35   $152.30  
  Purchase #2 $67.80   8.438%   $73.521   $73.52   $73.50   $73.50  
  Purchase #3 $15.92   6.859%   $17.012   $17.01   $17.00   $17.00  
  Purchase #4 $43.53   7.781%   $46.9171   $46.92   $46.90   $46.90  
  Purchase #5 $245.70   6.730%   $262.2356   $262.24   $262.25   $262.20  
  Purchase #6 $232.40   9.331%   $254.0852   $254.09   $254.10   $254.10  
  Purchase #7 $241.65   5.209%   $254.2375   $254.24   $254.25   $254.20  
  7 purchase totals = $994.70       $1,060.3403   $1,060.35   $1,060.35   $1,060.20