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 $47.93   4.789%   $50.2254   $50.23   $50.25   $50.20  
  Purchase #2 $214.75   13.248%   $243.2001   $243.20   $243.20   $243.20  
  Purchase #3 $90.34   13.275%   $102.3326   $102.33   $102.35   $102.30  
  Purchase #4 $156.32   6.567%   $166.5855   $166.59   $166.60   $166.60  
  Purchase #5 $245.30   11.749%   $274.1203   $274.12   $274.10   $274.10  
  Purchase #6 $107.62   11.415%   $119.9048   $119.90   $119.90   $119.90  
  Purchase #7 $201.80   9.249%   $220.4645   $220.46   $220.45   $220.50  
  7 purchase totals = $1,064.06       $1,176.8332   $1,176.83   $1,176.85   $1,176.80