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 $44.62   6.434%   $47.4909   $47.49   $47.50   $47.50  
  Purchase #2 $56.85   13.527%   $64.5401   $64.54   $64.55   $64.50  
  Purchase #3 $99.41   8.283%   $107.6441   $107.64   $107.65   $107.60  
  Purchase #4 $171.85   13.437%   $194.9415   $194.94   $194.95   $194.90  
  Purchase #5 $232.92   12.664%   $262.417   $262.42   $262.40   $262.40  
  Purchase #6 $237.29   11.636%   $264.9011   $264.90   $264.90   $264.90  
  Purchase #7 $60.96   13.764%   $69.3505   $69.35   $69.35   $69.40  
  7 purchase totals = $903.90       $1,011.2852   $1,011.28   $1,011.30   $1,011.20