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 $72.79   6.408%   $77.4544   $77.45   $77.45   $77.50  
  Purchase #2 $152.49   9.143%   $166.4322   $166.43   $166.45   $166.40  
  Purchase #3 $34.85   10.545%   $38.5249   $38.52   $38.50   $38.50  
  Purchase #4 $173.32   10.770%   $191.9866   $191.99   $192.00   $192.00  
  Purchase #5 $196.86   6.850%   $210.3449   $210.34   $210.35   $210.30  
  Purchase #6 $196.41   7.469%   $211.0799   $211.08   $211.10   $211.10  
  Purchase #7 $65.47   6.124%   $69.4794   $69.48   $69.50   $69.50  
  7 purchase totals = $892.19       $965.3023   $965.29   $965.35   $965.30