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 $41.80   5.278%   $44.0062   $44.01   $44.00   $44.00  
  Purchase #2 $134.32   10.330%   $148.1953   $148.20   $148.20   $148.20  
  Purchase #3 $120.44   11.211%   $133.9425   $133.94   $133.95   $133.90  
  Purchase #4 $47.98   4.372%   $50.0777   $50.08   $50.10   $50.10  
  Purchase #5 $55.27   9.347%   $60.4361   $60.44   $60.45   $60.40  
  Purchase #6 $121.54   4.262%   $126.72   $126.72   $126.70   $126.70  
  Purchase #7 $201.46   6.118%   $213.7853   $213.79   $213.80   $213.80  
  7 purchase totals = $722.81       $777.1631   $777.18   $777.20   $777.10