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 $197.26   9.726%   $216.4455   $216.45   $216.45   $216.40  
  Purchase #2 $23.84   6.315%   $25.3455   $25.35   $25.35   $25.30  
  Purchase #3 $188.74   8.658%   $205.0811   $205.08   $205.10   $205.10  
  Purchase #4 $57.89   13.264%   $65.5685   $65.57   $65.55   $65.60  
  Purchase #5 $72.83   11.604%   $81.2812   $81.28   $81.30   $81.30  
  Purchase #6 $161.69   6.515%   $172.2241   $172.22   $172.20   $172.20  
  Purchase #7 $170.70   8.372%   $184.991   $184.99   $185.00   $185.00  
  7 purchase totals = $872.95       $950.9369   $950.94   $950.95   $950.90