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 $139.60   7.750%   $150.419   $150.42   $150.40   $150.40  
  Purchase #2 $143.90   13.827%   $163.7971   $163.80   $163.80   $163.80  
  Purchase #3 $137.79   5.758%   $145.7239   $145.72   $145.70   $145.70  
  Purchase #4 $64.91   3.839%   $67.4019   $67.40   $67.40   $67.40  
  Purchase #5 $47.81   11.109%   $53.1212   $53.12   $53.10   $53.10  
  Purchase #6 $180.65   11.158%   $200.8069   $200.81   $200.80   $200.80  
  Purchase #7 $79.78   9.485%   $87.3471   $87.35   $87.35   $87.30  
  7 purchase totals = $794.44       $868.6171   $868.62   $868.55   $868.50