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 $66.54   3.136%   $68.6267   $68.63   $68.65   $68.60  
  Purchase #2 $155.37   9.869%   $170.7035   $170.70   $170.70   $170.70  
  Purchase #3 $67.44   11.404%   $75.1309   $75.13   $75.15   $75.10  
  Purchase #4 $174.25   12.822%   $196.5923   $196.59   $196.60   $196.60  
  Purchase #5 $181.62   13.624%   $206.3639   $206.36   $206.35   $206.40  
  Purchase #6 $123.83   8.196%   $133.9791   $133.98   $134.00   $134.00  
  Purchase #7 $130.53   11.529%   $145.5788   $145.58   $145.60   $145.60  
  7 purchase totals = $899.58       $996.9752   $996.97   $997.05   $997.00