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 $48.76   9.372%   $53.3298   $53.33   $53.35   $53.30  
  Purchase #2 $211.32   13.783%   $240.4462   $240.45   $240.45   $240.40  
  Purchase #3 $69.85   9.252%   $76.3125   $76.31   $76.30   $76.30  
  Purchase #4 $195.62   5.779%   $206.9249   $206.92   $206.90   $206.90  
  Purchase #5 $249.29   5.295%   $262.4899   $262.49   $262.50   $262.50  
  Purchase #6 $180.79   13.547%   $205.2816   $205.28   $205.30   $205.30  
  Purchase #7 $141.66   12.699%   $159.6494   $159.65   $159.65   $159.60  
  7 purchase totals = $1,097.29       $1,204.4343   $1,204.43   $1,204.45   $1,204.30