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 $59.30   9.590%   $64.9869   $64.99   $65.00   $65.00  
  Purchase #2 $20.35   4.651%   $21.2965   $21.30   $21.30   $21.30  
  Purchase #3 $65.66   13.703%   $74.6574   $74.66   $74.65   $74.70  
  Purchase #4 $27.63   12.543%   $31.0956   $31.10   $31.10   $31.10  
  Purchase #5 $81.70   11.772%   $91.3177   $91.32   $91.30   $91.30  
  Purchase #6 $30.69   4.289%   $32.0063   $32.01   $32.00   $32.00  
  Purchase #7 $128.99   12.380%   $144.959   $144.96   $144.95   $145.00  
  7 purchase totals = $414.32       $460.3194   $460.34   $460.30   $460.40