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 $210.82   10.320%   $232.5766   $232.58   $232.60   $232.60  
  Purchase #2 $138.64   6.450%   $147.5823   $147.58   $147.60   $147.60  
  Purchase #3 $48.63   7.104%   $52.0847   $52.08   $52.10   $52.10  
  Purchase #4 $226.58   9.241%   $247.5183   $247.52   $247.50   $247.50  
  Purchase #5 $88.66   4.852%   $92.9618   $92.96   $92.95   $93.00  
  Purchase #6 $107.37   3.705%   $111.3481   $111.35   $111.35   $111.30  
  Purchase #7 $127.34   6.286%   $135.3446   $135.34   $135.35   $135.30  
  7 purchase totals = $948.04       $1,019.4164   $1,019.41   $1,019.45   $1,019.40