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 $220.59   10.194%   $243.0769   $243.08   $243.10   $243.10  
  Purchase #2 $86.87   5.426%   $91.5836   $91.58   $91.60   $91.60  
  Purchase #3 $152.67   8.799%   $166.1034   $166.10   $166.10   $166.10  
  Purchase #4 $175.87   13.729%   $200.0152   $200.02   $200.00   $200.00  
  Purchase #5 $143.65   11.865%   $160.6941   $160.69   $160.70   $160.70  
  Purchase #6 $60.80   6.873%   $64.9788   $64.98   $65.00   $65.00  
  Purchase #7 $150.88   10.653%   $166.9532   $166.95   $166.95   $167.00  
  7 purchase totals = $991.33       $1,093.4052   $1,093.40   $1,093.45   $1,093.50