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 $87.60   10.728%   $96.9977   $97.00   $97.00   $97.00  
  Purchase #2 $176.46   12.170%   $197.9352   $197.94   $197.95   $197.90  
  Purchase #3 $206.88   9.617%   $226.7756   $226.78   $226.80   $226.80  
  Purchase #4 $202.46   11.848%   $226.4475   $226.45   $226.45   $226.40  
  Purchase #5 $206.37   12.658%   $232.4923   $232.49   $232.50   $232.50  
  Purchase #6 $148.48   9.363%   $162.3822   $162.38   $162.40   $162.40  
  Purchase #7 $44.93   9.584%   $49.2361   $49.24   $49.25   $49.20  
  7 purchase totals = $1,073.18       $1,192.2666   $1,192.28   $1,192.35   $1,192.20