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 $61.34   7.566%   $65.981   $65.98   $66.00   $66.00  
  Purchase #2 $21.63   4.327%   $22.5659   $22.57   $22.55   $22.60  
  Purchase #3 $139.28   6.141%   $147.8332   $147.83   $147.85   $147.80  
  Purchase #4 $242.67   8.196%   $262.5592   $262.56   $262.55   $262.60  
  Purchase #5 $135.58   12.310%   $152.2699   $152.27   $152.25   $152.30  
  Purchase #6 $25.84   5.793%   $27.3369   $27.34   $27.35   $27.30  
  Purchase #7 $99.96   8.764%   $108.7205   $108.72   $108.70   $108.70  
  7 purchase totals = $726.30       $787.2666   $787.27   $787.25   $787.30