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 $93.86   3.212%   $96.8748   $96.87   $96.85   $96.90  
  Purchase #2 $45.68   11.443%   $50.9072   $50.91   $50.90   $50.90  
  Purchase #3 $186.44   5.501%   $196.6961   $196.70   $196.70   $196.70  
  Purchase #4 $230.98   11.133%   $256.695   $256.70   $256.70   $256.70  
  Purchase #5 $75.42   7.216%   $80.8623   $80.86   $80.85   $80.90  
  Purchase #6 $74.58   13.331%   $84.5223   $84.52   $84.50   $84.50  
  Purchase #7 $118.98   4.663%   $124.528   $124.53   $124.55   $124.50  
  7 purchase totals = $825.94       $891.0857   $891.09   $891.05   $891.10