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 $47.51   11.486%   $52.967   $52.97   $52.95   $53.00  
  Purchase #2 $206.88   11.337%   $230.334   $230.33   $230.35   $230.30  
  Purchase #3 $237.33   6.562%   $252.9036   $252.90   $252.90   $252.90  
  Purchase #4 $237.79   13.492%   $269.8726   $269.87   $269.85   $269.90  
  Purchase #5 $27.66   8.450%   $29.9973   $30.00   $30.00   $30.00  
  Purchase #6 $41.66   8.530%   $45.2136   $45.21   $45.20   $45.20  
  Purchase #7 $101.92   9.242%   $111.3394   $111.34   $111.35   $111.30  
  7 purchase totals = $900.75       $992.6275   $992.62   $992.60   $992.60