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 $188.79   8.579%   $204.9863   $204.99   $205.00   $205.00  
  Purchase #2 $213.87   7.319%   $229.5231   $229.52   $229.50   $229.50  
  Purchase #3 $240.59   13.382%   $272.7858   $272.79   $272.80   $272.80  
  Purchase #4 $43.69   7.807%   $47.1009   $47.10   $47.10   $47.10  
  Purchase #5 $203.76   3.381%   $210.6491   $210.65   $210.65   $210.60  
  Purchase #6 $60.80   13.796%   $69.188   $69.19   $69.20   $69.20  
  Purchase #7 $41.39   4.487%   $43.2472   $43.25   $43.25   $43.20  
  7 purchase totals = $992.89       $1,077.4804   $1,077.49   $1,077.50   $1,077.40