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 $184.91   12.247%   $207.5559   $207.56   $207.55   $207.60  
  Purchase #2 $109.87   11.703%   $122.7281   $122.73   $122.75   $122.70  
  Purchase #3 $24.97   13.275%   $28.2848   $28.28   $28.30   $28.30  
  Purchase #4 $191.52   13.225%   $216.8485   $216.85   $216.85   $216.80  
  Purchase #5 $94.99   6.840%   $101.4873   $101.49   $101.50   $101.50  
  Purchase #6 $194.52   9.264%   $212.5403   $212.54   $212.55   $212.50  
  Purchase #7 $184.70   11.411%   $205.7761   $205.78   $205.80   $205.80  
  7 purchase totals = $985.48       $1,095.2210   $1,095.23   $1,095.30   $1,095.20