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 $45.41   13.633%   $51.6007   $51.60   $51.60   $51.60  
  Purchase #2 $191.48   9.416%   $209.5098   $209.51   $209.50   $209.50  
  Purchase #3 $201.66   5.198%   $212.1423   $212.14   $212.15   $212.10  
  Purchase #4 $145.51   12.252%   $163.3379   $163.34   $163.35   $163.30  
  Purchase #5 $38.72   11.179%   $43.0485   $43.05   $43.05   $43.00  
  Purchase #6 $128.99   6.814%   $137.7794   $137.78   $137.80   $137.80  
  Purchase #7 $227.56   4.739%   $238.3441   $238.34   $238.35   $238.30  
  7 purchase totals = $979.33       $1,055.7627   $1,055.76   $1,055.80   $1,055.60