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 $70.53   6.280%   $74.9593   $74.96   $74.95   $75.00  
  Purchase #2 $21.60   10.354%   $23.8365   $23.84   $23.85   $23.80  
  Purchase #3 $218.54   8.365%   $236.8209   $236.82   $236.80   $236.80  
  Purchase #4 $80.35   9.335%   $87.8507   $87.85   $87.85   $87.90  
  Purchase #5 $193.84   6.373%   $206.1934   $206.19   $206.20   $206.20  
  Purchase #6 $136.86   10.227%   $150.8567   $150.86   $150.85   $150.90  
  Purchase #7 $124.91   11.387%   $139.1335   $139.13   $139.15   $139.10  
  7 purchase totals = $846.63       $919.6510   $919.65   $919.65   $919.70