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 $20.26   11.850%   $22.6608   $22.66   $22.65   $22.70  
  Purchase #2 $51.55   7.654%   $55.4956   $55.50   $55.50   $55.50  
  Purchase #3 $136.40   6.426%   $145.1651   $145.17   $145.15   $145.20  
  Purchase #4 $170.38   9.807%   $187.0892   $187.09   $187.10   $187.10  
  Purchase #5 $12.34   11.847%   $13.8019   $13.80   $13.80   $13.80  
  Purchase #6 $70.51   5.621%   $74.4734   $74.47   $74.45   $74.50  
  Purchase #7 $29.68   4.787%   $31.1008   $31.10   $31.10   $31.10  
  7 purchase totals = $491.12       $529.7868   $529.79   $529.75   $529.90