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 $72.94   6.817%   $77.9123   $77.91   $77.90   $77.90  
  Purchase #2 $239.90   13.144%   $271.4325   $271.43   $271.45   $271.40  
  Purchase #3 $49.50   6.144%   $52.5413   $52.54   $52.55   $52.50  
  Purchase #4 $247.79   8.862%   $269.7491   $269.75   $269.75   $269.70  
  Purchase #5 $44.80   4.471%   $46.803   $46.80   $46.80   $46.80  
  Purchase #6 $145.52   10.593%   $160.9349   $160.93   $160.95   $160.90  
  Purchase #7 $80.67   3.383%   $83.3991   $83.40   $83.40   $83.40  
  7 purchase totals = $881.12       $962.7722   $962.76   $962.80   $962.60