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 $18.68   3.599%   $19.3523   $19.35   $19.35   $19.40  
  Purchase #2 $213.78   4.743%   $223.9196   $223.92   $223.90   $223.90  
  Purchase #3 $179.25   7.715%   $193.0791   $193.08   $193.10   $193.10  
  Purchase #4 $28.32   12.832%   $31.954   $31.95   $31.95   $32.00  
  Purchase #5 $39.78   12.313%   $44.6781   $44.68   $44.70   $44.70  
  Purchase #6 $203.47   8.528%   $220.8219   $220.82   $220.80   $220.80  
  Purchase #7 $180.43   6.845%   $192.7804   $192.78   $192.80   $192.80  
  7 purchase totals = $863.71       $926.5854   $926.58   $926.60   $926.70