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 $101.57   9.125%   $110.8383   $110.84   $110.85   $110.80  
  Purchase #2 $237.84   5.287%   $250.4146   $250.41   $250.40   $250.40  
  Purchase #3 $190.62   9.779%   $209.2607   $209.26   $209.25   $209.30  
  Purchase #4 $223.87   12.578%   $252.0284   $252.03   $252.05   $252.00  
  Purchase #5 $73.54   4.711%   $77.0045   $77.00   $77.00   $77.00  
  Purchase #6 $132.80   4.492%   $138.7654   $138.77   $138.75   $138.80  
  Purchase #7 $87.29   4.809%   $91.4878   $91.49   $91.50   $91.50  
  7 purchase totals = $1,047.53       $1,129.7997   $1,129.80   $1,129.80   $1,129.80