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 $211.41   10.733%   $234.1006   $234.10   $234.10   $234.10  
  Purchase #2 $6.48   3.423%   $6.7018   $6.70   $6.70   $6.70  
  Purchase #3 $56.40   9.392%   $61.6971   $61.70   $61.70   $61.70  
  Purchase #4 $58.68   7.490%   $63.0751   $63.08   $63.10   $63.10  
  Purchase #5 $191.61   9.510%   $209.8321   $209.83   $209.85   $209.80  
  Purchase #6 $80.60   4.381%   $84.1311   $84.13   $84.15   $84.10  
  Purchase #7 $200.66   9.284%   $219.2893   $219.29   $219.30   $219.30  
  7 purchase totals = $805.84       $878.8271   $878.83   $878.90   $878.80