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 $178.35   4.477%   $186.3347   $186.33   $186.35   $186.30  
  Purchase #2 $186.65   10.241%   $205.7648   $205.76   $205.75   $205.80  
  Purchase #3 $130.33   10.467%   $143.9716   $143.97   $143.95   $144.00  
  Purchase #4 $60.45   13.214%   $68.4379   $68.44   $68.45   $68.40  
  Purchase #5 $243.96   11.720%   $272.5521   $272.55   $272.55   $272.60  
  Purchase #6 $141.46   4.432%   $147.7295   $147.73   $147.75   $147.70  
  Purchase #7 $46.96   7.350%   $50.4116   $50.41   $50.40   $50.40  
  7 purchase totals = $988.16       $1,075.2022   $1,075.19   $1,075.20   $1,075.20