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 $64.54   11.225%   $71.7846   $71.78   $71.80   $71.80  
  Purchase #2 $175.93   12.295%   $197.5606   $197.56   $197.55   $197.60  
  Purchase #3 $232.27   6.195%   $246.6591   $246.66   $246.65   $246.70  
  Purchase #4 $43.38   10.830%   $48.0781   $48.08   $48.10   $48.10  
  Purchase #5 $197.71   10.753%   $218.9698   $218.97   $218.95   $219.00  
  Purchase #6 $103.95   8.176%   $112.449   $112.45   $112.45   $112.40  
  Purchase #7 $174.30   6.454%   $185.5493   $185.55   $185.55   $185.50  
  7 purchase totals = $992.08       $1,081.0505   $1,081.05   $1,081.05   $1,081.10