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 $203.26   9.153%   $221.8644   $221.86   $221.85   $221.90  
  Purchase #2 $202.81   11.757%   $226.6544   $226.65   $226.65   $226.70  
  Purchase #3 $87.59   5.431%   $92.347   $92.35   $92.35   $92.30  
  Purchase #4 $40.25   8.211%   $43.5549   $43.55   $43.55   $43.60  
  Purchase #5 $69.73   4.633%   $72.9606   $72.96   $72.95   $73.00  
  Purchase #6 $37.33   5.184%   $39.2652   $39.27   $39.25   $39.30  
  Purchase #7 $247.47   8.520%   $268.5544   $268.55   $268.55   $268.60  
  7 purchase totals = $888.44       $965.2009   $965.19   $965.15   $965.40