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 $204.92   4.564%   $214.2725   $214.27   $214.25   $214.30  
  Purchase #2 $187.69   7.830%   $202.3861   $202.39   $202.40   $202.40  
  Purchase #3 $82.80   4.699%   $86.6908   $86.69   $86.70   $86.70  
  Purchase #4 $153.79   8.425%   $166.7468   $166.75   $166.75   $166.70  
  Purchase #5 $147.56   11.232%   $164.1339   $164.13   $164.15   $164.10  
  Purchase #6 $70.95   4.766%   $74.3315   $74.33   $74.35   $74.30  
  Purchase #7 $29.52   8.564%   $32.0481   $32.05   $32.05   $32.00  
  7 purchase totals = $877.23       $940.6097   $940.61   $940.65   $940.50