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 $57.98   5.424%   $61.1248   $61.12   $61.10   $61.10  
  Purchase #2 $43.47   4.401%   $45.3831   $45.38   $45.40   $45.40  
  Purchase #3 $96.57   12.856%   $108.985   $108.99   $109.00   $109.00  
  Purchase #4 $200.38   5.852%   $212.1062   $212.11   $212.10   $212.10  
  Purchase #5 $218.33   11.381%   $243.1781   $243.18   $243.20   $243.20  
  Purchase #6 $109.88   11.609%   $122.636   $122.64   $122.65   $122.60  
  Purchase #7 $168.48   5.646%   $177.9924   $177.99   $178.00   $178.00  
  7 purchase totals = $895.09       $971.4056   $971.41   $971.45   $971.40