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 $83.77   13.845%   $95.368   $95.37   $95.35   $95.40  
  Purchase #2 $50.74   7.470%   $54.5303   $54.53   $54.55   $54.50  
  Purchase #3 $63.66   12.835%   $71.8308   $71.83   $71.85   $71.80  
  Purchase #4 $195.93   7.417%   $210.4621   $210.46   $210.45   $210.50  
  Purchase #5 $200.82   7.630%   $216.1426   $216.14   $216.15   $216.10  
  Purchase #6 $5.26   13.582%   $5.9744   $5.97   $5.95   $6.00  
  Purchase #7 $54.74   3.591%   $56.7057   $56.71   $56.70   $56.70  
  7 purchase totals = $654.92       $711.0139   $711.01   $711.00   $711.00