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 $177.56   9.123%   $193.7588   $193.76   $193.75   $193.80  
  Purchase #2 $212.70   8.292%   $230.3371   $230.34   $230.35   $230.30  
  Purchase #3 $205.93   12.564%   $231.803   $231.80   $231.80   $231.80  
  Purchase #4 $36.50   5.709%   $38.5838   $38.58   $38.60   $38.60  
  Purchase #5 $51.85   9.200%   $56.6202   $56.62   $56.60   $56.60  
  Purchase #6 $124.26   8.526%   $134.8544   $134.85   $134.85   $134.90  
  Purchase #7 $132.49   11.311%   $147.4759   $147.48   $147.50   $147.50  
  7 purchase totals = $941.29       $1,033.4332   $1,033.43   $1,033.45   $1,033.50